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Human Reproduction – CBSE NCERT Study Resources

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12th

12th - Biology

Human Reproduction

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Overview

The chapter "Human Reproduction" in the CBSE Grade 12 Biology curriculum covers the reproductive processes in humans, including the male and female reproductive systems, gametogenesis, menstrual cycle, fertilization, implantation, pregnancy, and parturition. It also discusses lactation and reproductive health.

Male Reproductive System

The male reproductive system consists of primary sex organs (testes) and accessory ducts (epididymis, vas deferens, ejaculatory duct, and urethra). The testes produce sperm and secrete testosterone. Accessory glands include seminal vesicles, prostate gland, and bulbourethral glands.

Gametogenesis: The process of formation of gametes (sperm in males and ova in females) is called gametogenesis.

Female Reproductive System

The female reproductive system includes ovaries, oviducts, uterus, cervix, and vagina. The ovaries produce ova and secrete estrogen and progesterone. The uterus supports fetal development during pregnancy.

Menstrual Cycle

The menstrual cycle is a series of cyclic changes in the ovaries and uterus, regulated by hormones like FSH, LH, estrogen, and progesterone. It consists of the menstrual phase, follicular phase, ovulatory phase, and luteal phase.

Ovulation: The release of a mature ovum from the ovary around the 14th day of the menstrual cycle.

Fertilization and Implantation

Fertilization occurs when a sperm fuses with an ovum in the fallopian tube, forming a zygote. The zygote undergoes cleavage and forms a blastocyst, which implants into the uterine wall.

Pregnancy and Embryonic Development

After implantation, the placenta forms, providing nutrition and oxygen to the developing embryo. The embryonic stages include gastrulation, organogenesis, and fetal development.

Parturition and Lactation

Parturition is the process of childbirth, regulated by oxytocin. Lactation involves the production of milk by mammary glands, stimulated by prolactin.

Colostrum: The first milk produced after childbirth, rich in antibodies and essential nutrients.

Reproductive Health

This section discusses the importance of reproductive health, family planning, contraception, and sexually transmitted infections (STIs).

All Question Types with Solutions – CBSE Exam Pattern

Explore a complete set of CBSE-style questions with detailed solutions, categorized by marks and question types. Ideal for exam preparation, revision and practice.

Very Short Answer (1 Mark) – with Solutions (CBSE Pattern)

These are 1-mark questions requiring direct, concise answers. Ideal for quick recall and concept clarity.

Question 1:
What is the significance of corpus luteum?
Answer:
Secretes progesterone to maintain pregnancy.
Question 2:
Define menarche.
Answer:
Definition: First menstrual cycle at puberty.
Question 3:
Name the phase of menstrual cycle when ovulation occurs.
Answer:
Proliferative phase (Day 10-14).
Question 4:
What causes lactation post-delivery?
Answer:
Prolactin from anterior pituitary.
Question 5:
Which structure forms the placental barrier?
Answer:
Chorionic villi and uterine tissue.
Question 6:
State one function of seminal vesicles.
Answer:
Secrete fructose-rich fluid for sperm motility.
Question 7:
Define gametogenesis.
Answer:
Definition: Process of formation of gametes (sperm/ova) in gonads.
Question 8:
Name the hormone that stimulates spermatogenesis.
Answer:
Follicle Stimulating Hormone (FSH).
Question 9:
What is the function of acrosome in sperm?
Answer:
Contains enzymes to dissolve zona pellucida for fertilization.
Question 10:
Where does fertilization occur in humans?
Answer:
Ampulla of the fallopian tube.
Question 11:
State the role of Leydig cells.
Answer:
Secrete testosterone in testes.
Question 12:
What is implantation?
Answer:
Definition: Embedding of blastocyst into uterine endometrium.
Question 13:
Identify the membrane that prevents polyspermy.
Answer:
Zona pellucida hardens after fertilization.
Question 14:
Which cells secrete hCG during pregnancy?
Answer:
Syncytiotrophoblast cells of placenta.
Question 15:
Name the hormone responsible for the development of secondary sexual characters in males.
Answer:
Testosterone is the hormone responsible for the development of secondary sexual characters in males, such as deepening of voice and growth of facial hair.
Question 16:
What is the function of the corpus luteum in the female reproductive system?
Answer:

The corpus luteum secretes progesterone, which prepares the endometrium for implantation of the fertilized ovum and maintains pregnancy.

Question 17:
Define spermatogenesis.
Answer:

Spermatogenesis is the process of formation of spermatozoa (sperms) from the germinal epithelial cells of the seminiferous tubules in the testes.

Question 18:
What is the role of the acrosome in sperm?
Answer:

The acrosome contains enzymes like hyaluronidase and acrosin, which help the sperm penetrate the ovum during fertilization.

Question 19:
Name the structure that connects the fetus to the uterine wall.
Answer:

The placenta connects the fetus to the uterine wall, facilitating nutrient and gas exchange between mother and fetus.

Question 20:
What is the significance of the LH surge in the menstrual cycle?
Answer:

The LH surge triggers ovulation, causing the release of the mature ovum from the Graafian follicle.

Question 21:
Where does fertilization typically occur in humans?
Answer:

Fertilization typically occurs in the fallopian tube (oviduct), specifically in the ampullary-isthmic junction.

Question 22:
What is the function of epididymis in the male reproductive system?
Answer:

The epididymis stores and matures sperms, providing them with motility and fertilization capacity.

Question 23:
Name the membrane that surrounds the ovum and prevents polyspermy.
Answer:

The zona pellucida surrounds the ovum and undergoes changes to prevent polyspermy after fertilization.

Question 24:
What is the role of oxytocin during childbirth?
Answer:

Oxytocin stimulates powerful contractions of the uterine muscles during labor, aiding in childbirth.

Question 25:
Define implantation in human reproduction.
Answer:

Implantation is the process by which the blastocyst attaches to the endometrium of the uterus for further development.

Question 26:
What is the function of Sertoli cells in the testes?
Answer:

Sertoli cells provide nutrition and support to developing sperms and secrete the hormone inhibin.

Very Short Answer (2 Marks) – with Solutions (CBSE Pattern)

These 2-mark questions test key concepts in a brief format. Answers are expected to be accurate and slightly descriptive.

Question 1:
Name the hormone responsible for the development of secondary sexual characters in males.
Answer:

The hormone responsible for the development of secondary sexual characters in males is testosterone. It is secreted by the Leydig cells of the testes and promotes features like facial hair, deepening of voice, and muscle growth.

Question 2:
What is the function of the acrosome in a sperm?
Answer:

The acrosome is a cap-like structure on the sperm head containing digestive enzymes like hyaluronidase and acrosin. These enzymes help the sperm penetrate the zona pellucida of the ovum during fertilization.

Question 3:
What is the role of LH in the female reproductive system?
Answer:

Luteinizing Hormone (LH) triggers ovulation (release of the ovum from the ovary) and stimulates the ruptured follicle to form the corpus luteum, which secretes progesterone to maintain pregnancy.

Question 4:
Why is the endometrium essential for reproduction?
Answer:

The endometrium is the inner lining of the uterus that thickens during the menstrual cycle to provide a nutrient-rich layer for the implantation of the fertilized egg (blastocyst). If fertilization occurs, it supports the developing embryo.

Question 5:
Differentiate between zygote and morula.
Answer:

  • Zygote: Formed by the fusion of sperm and ovum; it is a single-celled diploid structure.
  • Morula: A solid ball of 8–16 cells formed by cleavage divisions of the zygote; it precedes the blastocyst stage.

Question 6:
What is the significance of the corpus luteum?
Answer:

The corpus luteum is a temporary endocrine structure formed after ovulation. It secretes progesterone and estrogen to:
1. Maintain the endometrium for implantation
2. Inhibit further ovulation during pregnancy.

Question 7:
Name the cells that nourish the developing sperm in the testes.
Answer:

The Sertoli cells (or nurse cells) in the seminiferous tubules provide nutrition and support to the developing sperms during spermatogenesis.

Question 8:
Explain the term implantation.
Answer:

Implantation is the process where the blastocyst (early embryo) attaches and embeds into the endometrium of the uterus around 6–7 days after fertilization. It marks the beginning of pregnancy.

Question 9:
What is the function of hCG during pregnancy?
Answer:

Human Chorionic Gonadotropin (hCG) is secreted by the placenta. It:
1. Maintains the corpus luteum to secrete progesterone
2. Detected in pregnancy tests as an early marker.

Question 10:
Why does the menstrual cycle stop during pregnancy?
Answer:

During pregnancy, high levels of progesterone and estrogen (secreted by the corpus luteum and later the placenta) inhibit the release of FSH and LH, preventing ovulation and menstruation to support the growing fetus.

Question 11:
Define spermatogenesis and where does it occur?
Answer:

Spermatogenesis is the process of formation of spermatozoa (sperms) from spermatogonia in the seminiferous tubules of the testes. It involves mitosis, meiosis, and spermiogenesis.

Question 12:
What is the role of FSH in the male reproductive system?
Answer:

Follicle-stimulating hormone (FSH) stimulates the Sertoli cells in the testes to promote spermatogenesis by providing nutrients to developing sperm cells.

Question 13:
Explain the significance of the acrosome in sperm.
Answer:

The acrosome is a cap-like structure filled with digestive enzymes (hyaluronidase and acrosin) that help the sperm penetrate the zona pellucida of the ovum during fertilization.

Question 14:
What is oogenesis? Mention its key difference from spermatogenesis.
Answer:

Oogenesis is the process of formation of a mature ovum from oogonia in the ovaries. Unlike spermatogenesis, it results in one functional ovum and polar bodies due to unequal cytoplasmic division.

Question 15:
Name the structure that connects the fetus to the uterine wall and list its functions.
Answer:

The placenta connects the fetus to the uterine wall. Its functions include:

  • Nutrient and gas exchange
  • Waste removal
  • Hormone secretion (hCG, progesterone)

Question 16:
What is implantation? When does it occur in humans?
Answer:

Implantation is the embedding of the blastocyst into the endometrium of the uterus. It occurs 6-7 days after fertilization in humans.

Question 17:
Why is the scrotum located outside the abdominal cavity?
Answer:

The scrotum maintains a temperature 2-3°C lower than the body, which is essential for spermatogenesis as higher temperatures impair sperm production.

Question 18:
What is the function of LH in females?
Answer:

Luteinizing hormone (LH) triggers ovulation and stimulates the ruptured follicle to form the corpus luteum, which secretes progesterone.

Short Answer (3 Marks) – with Solutions (CBSE Pattern)

These 3-mark questions require brief explanations and help assess understanding and application of concepts.

Question 1:
Explain the role of Leydig cells in the male reproductive system.
Answer:

Leydig cells, also known as interstitial cells, are located in the testes between the seminiferous tubules.
Their primary function is to secrete testosterone, the male sex hormone.
Testosterone plays a crucial role in:

  • Development of male secondary sexual characteristics (e.g., facial hair, deep voice).
  • Spermatogenesis (sperm production).
  • Maintaining libido and overall male reproductive health.

Question 2:
Describe the process of oogenesis in human females.
Answer:

Oogenesis is the formation of mature ova (eggs) in the ovaries.
The process involves:
1. Multiplication phase: Oogonia (diploid cells) multiply by mitosis during fetal development.
2. Growth phase: Some oogonia grow into primary oocytes and enter meiosis I but halt at prophase I until puberty.
3. Maturation phase: After puberty, one primary oocyte completes meiosis I monthly, forming a secondary oocyte and a polar body.
The secondary oocyte arrests at metaphase II and is released during ovulation. Fertilization triggers completion of meiosis II, forming a mature ovum and another polar body.

Question 3:
What is the significance of the acrosome in sperm?
Answer:

The acrosome is a cap-like structure on the sperm head containing hydrolytic enzymes like hyaluronidase and acrosin.
Its functions include:

  • Digesting the outer layers (zona pellucida and corona radiata) of the egg during fertilization.
  • Facilitating sperm penetration for successful fusion with the egg.
Without the acrosome, sperm cannot fertilize the ovum.

Question 4:
How does the corpus luteum contribute to pregnancy?
Answer:

The corpus luteum forms from the ruptured ovarian follicle after ovulation.
It secretes:

  • Progesterone: Maintains the endometrium for embryo implantation.
  • Estrogen: Supports uterine lining and inhibits further ovulation.
If fertilization occurs, the corpus luteum persists due to hCG (human chorionic gonadotropin) from the embryo. Otherwise, it degenerates, causing menstruation.

Question 5:
Differentiate between zygote, morula, and blastocyst.
Answer:

  • Zygote: A diploid cell formed by fusion of sperm and egg; undergoes cleavage.
  • Morula: A solid 16-cell stage (resembling a mulberry) formed after 4-5 cleavage divisions.
  • Blastocyst: A hollow ball of cells with:
    - Trophoblast (outer layer for implantation).
    - Inner cell mass (forms the embryo).
These stages occur during early embryonic development.

Question 6:
Explain the function of placenta during pregnancy.
Answer:

The placenta is a temporary organ that:

  • Facilitates nutrient and oxygen exchange between mother and fetus.
  • Removes waste (e.g., CO2) from fetal blood.
  • Produces hormones like hCG, progesterone, and estrogen to sustain pregnancy.
  • Acts as a barrier against pathogens (though not all).
It connects via the umbilical cord and is expelled after birth.

Question 7:
Explain the role of Leydig cells in the male reproductive system.
Answer:

Leydig cells, also known as interstitial cells, are located in the testes between the seminiferous tubules. Their primary role is to produce and secrete testosterone, the male sex hormone.

Testosterone is crucial for:

  • Development of male secondary sexual characteristics (e.g., facial hair, deep voice).
  • Spermatogenesis (sperm production) by stimulating the seminiferous tubules.
  • Maintaining libido and overall male reproductive health.
Without Leydig cells, proper hormonal balance and reproductive functions would be impaired.

Question 8:
Describe the process of oogenesis in human females.
Answer:

Oogenesis is the process of formation of mature female gametes (ova) in the ovaries. It occurs in three phases:

1. Multiplication Phase: During fetal development, oogonia (diploid cells) multiply by mitosis.
2. Growth Phase: Some oogonia grow into primary oocytes and enter meiosis I but arrest at prophase I until puberty.
3. Maturation Phase: After puberty, one primary oocyte completes meiosis I monthly, forming a secondary oocyte (haploid) and a polar body. The secondary oocyte arrests at metaphase II and is released during ovulation. Fertilization triggers completion of meiosis II, forming a mature ovum.

Question 9:
What is the significance of the acrosome in sperm?
Answer:

The acrosome is a cap-like structure on the sperm head containing digestive enzymes like hyaluronidase and acrosin. Its functions include:

  • Penetrating the zona pellucida of the ovum during fertilization by dissolving its protective layers.
  • Facilitating sperm-egg fusion by exposing binding proteins on the sperm membrane.
Without the acrosome, sperm cannot fertilize the egg, making it essential for successful reproduction.

Question 10:
How does the corpus luteum contribute to pregnancy?
Answer:

The corpus luteum is a temporary endocrine structure formed from the ruptured ovarian follicle after ovulation. It secretes:

  • Progesterone: Maintains the uterine endometrium for embryo implantation and prevents menstruation.
  • Estrogen: Supports endometrial growth and inhibits FSH/LH to prevent further ovulation.
If fertilization occurs, the corpus luteum persists due to hCG (from the embryo) until the placenta takes over hormone production. Without it, early pregnancy cannot be sustained.

Question 11:
Differentiate between zygote and morula in early embryonic development.
Answer:

Zygote:

  • Forms immediately after fertilization (fusion of sperm and ovum).
  • Diploid (2n) and single-celled.
  • Undergoes cleavage to form blastomeres.
Morula:
  • Develops after 4-5 days of zygote cleavage.
  • Solid ball of 16-32 cells (blastomeres).
  • Precedes the blastocyst stage, which implants in the uterus.
Both stages are critical for early development but differ in structure and timing.

Question 12:
Explain the function of placental lactogen during pregnancy.
Answer:

Placental lactogen (hPL) is a hormone secreted by the placenta during pregnancy. Its roles include:

  • Metabolic regulation: Increases maternal blood glucose levels by reducing insulin sensitivity, ensuring fetal energy supply.
  • Mammary gland development: Prepares breasts for lactation by stimulating milk-producing tissues.
  • Fetal growth support: Enhances nutrient availability by breaking down maternal fats.
hPL works alongside progesterone and estrogen to sustain pregnancy and support fetal development.

Long Answer (5 Marks) – with Solutions (CBSE Pattern)

These 5-mark questions are descriptive and require detailed, structured answers with proper explanation and examples.

Question 1:
Explain the process of spermatogenesis with reference to the role of Sertoli cells and Leydig cells.
Answer:
Theoretical Framework

Spermatogenesis is the process of sperm formation in the seminiferous tubules. It involves mitosis, meiosis, and spermiogenesis. Sertoli cells provide nourishment and structural support, while Leydig cells secrete testosterone.

Evidence Analysis
  • Our textbook shows spermatogonia divide mitotically to form primary spermatocytes.
  • Meiosis I reduces chromosome number, forming secondary spermatocytes.
  • Spermiogenesis transforms spermatids into mature sperm.
Critical Evaluation

Testosterone from Leydig cells is crucial for meiosis, while Sertoli cells release inhibin for feedback regulation. Disruptions can lead to infertility.

Question 2:
Describe the hormonal regulation of the menstrual cycle, emphasizing the roles of FSH, LH, estrogen, and progesterone.
Answer:
Theoretical Framework

The menstrual cycle is regulated by the hypothalamus-pituitary-ovary axis. FSH stimulates follicular growth, while LH triggers ovulation. Estrogen and progesterone prepare the endometrium.

Evidence Analysis
  • FSH peaks in the follicular phase, developing Graafian follicles.
  • LH surge causes ovulation, forming the corpus luteum.
  • Progesterone maintains the endometrium for implantation.
Critical Evaluation

Imbalance in these hormones can cause disorders like PCOS. Our textbook highlights feedback loops involving GnRH.

Question 3:
Compare oogenesis and spermatogenesis in terms of timing, meiotic divisions, and gamete production.
Answer:
Theoretical Framework

Oogenesis produces one ovum per cycle, while spermatogenesis yields four sperm. Oogenesis begins prenatally and completes after puberty, unlike spermatogenesis.

Evidence Analysis
  • Primary oocytes arrest in prophase I until puberty.
  • Spermatocytes undergo continuous meiosis post-puberty.
  • Polar bodies form in oogenesis, reducing cytoplasmic content.
Critical Evaluation

This asymmetry ensures nutrient-rich ova for embryo development. Our textbook notes evolutionary advantages in gamete specialization.

Question 4:
Analyze the implantation process and the role of human chorionic gonadotropin (hCG) in pregnancy maintenance.
Answer:
Theoretical Framework

Implantation occurs when the blastocyst attaches to the endometrium. hCG rescues the corpus luteum, sustaining progesterone secretion.

Evidence Analysis
  • Trophoblast cells invade the endometrium, forming chorionic villi.
  • hCG is detectable in urine, used in pregnancy tests.
  • Progesterone prevents menstruation and supports placental development.
Critical Evaluation

Low hCG levels may indicate ectopic pregnancy. Our textbook emphasizes hCG's role in early pregnancy diagnostics.

Question 5:
Discuss the structure and functions of the placenta, including its role in nutrient exchange and hormone production.
Answer:
Theoretical Framework

The placenta is a fetomaternal organ with chorionic villi bathed in maternal blood. It facilitates nutrient exchange and secretes hormones like hPL and estrogen.

Evidence Analysis
  • Villi increase surface area for diffusion of O2 and glucose.
  • hPL regulates maternal metabolism for fetal growth.
  • Estrogen prepares mammary glands for lactation.
Critical Evaluation

Placental insufficiency can cause intrauterine growth restriction. Our textbook shows its endocrine role parallels pituitary function.

Question 6:
Explain the spermatogenesis process in human males, highlighting the role of Sertoli cells and Leydig cells.
Answer:
Theoretical Framework

Spermatogenesis is the process of sperm production in the seminiferous tubules. Our textbook shows it involves mitosis, meiosis, and spermiogenesis.

Evidence Analysis
  • Sertoli cells provide nourishment and support to developing spermatids.
  • Leydig cells secrete testosterone, crucial for meiosis.
Critical Evaluation

Without Sertoli cells, spermatids would not mature. Leydig cell dysfunction leads to low testosterone and infertility.

Future Implications

Research on these cells may improve treatments for male infertility.

Question 7:
Describe the menstrual cycle phases, emphasizing hormonal regulation by FSH, LH, and progesterone.
Answer:
Theoretical Framework

The menstrual cycle has follicular, ovulatory, and luteal phases. Our textbook shows hormones tightly regulate each stage.

Evidence Analysis
  • FSH stimulates follicular growth.
  • LH surge triggers ovulation.
  • Progesterone thickens the endometrium.
Critical Evaluation

Imbalance in these hormones causes disorders like PCOS. Current data shows 1 in 10 women face such issues.

Future Implications

Understanding hormonal feedback can lead to better contraceptive methods.

Question 8:
Compare placental and non-placental reproduction, focusing on nutrient exchange and waste removal mechanisms.
Answer:
Theoretical Framework

Placental mammals (e.g., humans) use a placenta for fetal support, while non-placental (e.g., marsupials) lack this structure.

Evidence Analysis
  • Placental: Nutrients diffuse via chorionic villi.
  • Non-placental: Yolk sac sustains early development.
Critical Evaluation

Placental efficiency allows longer gestation. Current data shows human placenta transfers 30L blood/day.

Future Implications

Studying placental defects may reduce miscarriages.

Question 9:
Analyze the acrosomal reaction and cortical reaction during fertilization, explaining their roles in preventing polyspermy.
Answer:
Theoretical Framework

Fertilization involves sperm-egg fusion. Our textbook shows acrosomal and cortical reactions ensure single sperm entry.

Evidence Analysis
  • Acrosomal enzymes digest the zona pellucida.
  • Cortical granules harden the zona to block polyspermy.
Critical Evaluation

Failure causes triploidy (lethal). Advanced research uses zebrafish to study these mechanisms.

Future Implications

Understanding these reactions could improve IVF success rates.

Question 10:
Discuss assisted reproductive technologies (ART) like IVF and ZIFT, evaluating their ethical and medical challenges.
Answer:
Theoretical Framework

ART includes IVF (in vitro fertilization) and ZIFT (zygote intrafallopian transfer). Our textbook shows they help infertile couples.

Evidence Analysis
  • IVF: Eggs fertilized externally.
  • ZIFT: Zygote transferred to fallopian tube.
Critical Evaluation

Ethical issues include embryo disposal. Medically, multiple pregnancies risk maternal health.

Future Implications

Stricter ART regulations may balance success rates and ethics.

Question 11:
Describe the process of spermatogenesis in human males with a labeled diagram. Explain the role of hormones in this process.
Answer:

Spermatogenesis is the process of sperm formation in the seminiferous tubules of the testes. It involves the following stages:

  • Multiplication Phase: Spermatogonia (diploid stem cells) divide mitotically to produce more spermatogonia.
  • Growth Phase: Some spermatogonia grow into primary spermatocytes (diploid).
  • Maturation Phase: Primary spermatocytes undergo meiosis I to form secondary spermatocytes (haploid), which then undergo meiosis II to form spermatids.
  • Spermiogenesis: Spermatids differentiate into mature spermatozoa (sperms) by losing excess cytoplasm and developing a tail.

Hormonal Regulation:

  • GnRH from the hypothalamus stimulates the pituitary to release LH and FSH.
  • LH acts on Leydig cells to secrete testosterone, which supports spermatogenesis.
  • FSH acts on Sertoli cells to provide nutrients and facilitate sperm maturation.

(Diagram: Labeled cross-section of seminiferous tubule showing spermatogonia, spermatocytes, spermatids, and spermatozoa.)

Question 12:
Explain the hormonal control of the menstrual cycle in human females. Highlight the roles of FSH, LH, estrogen, and progesterone.
Answer:

The menstrual cycle is regulated by a complex interplay of hormones:

  • Follicular Phase:
    FSH (Follicle-Stimulating Hormone) from the pituitary stimulates the growth of ovarian follicles and estrogen secretion.
    Rising estrogen thickens the endometrium and inhibits FSH (negative feedback).
  • Ovulatory Phase:
    High estrogen triggers a surge in LH (Luteinizing Hormone), causing ovulation (release of the ovum).
  • Luteal Phase:
    LH transforms the ruptured follicle into the corpus luteum, which secretes progesterone.
    Progesterone maintains the endometrium and inhibits FSH/LH (preventing new follicles).

If fertilization doesn't occur, the corpus luteum degenerates, causing a drop in progesterone and menstruation.

Question 13:
Explain the process of spermatogenesis in human males with a detailed diagram. Highlight the role of Sertoli cells and Leydig cells in this process.
Answer:

Spermatogenesis is the process of sperm production in the seminiferous tubules of the testes. It involves the following stages:

  • Multiplication Phase: Spermatogonia (diploid cells) undergo mitosis to increase in number.
  • Growth Phase: Spermatogonia grow into primary spermatocytes.
  • Maturation Phase: Primary spermatocytes undergo meiosis I to form secondary spermatocytes (haploid), which then undergo meiosis II to form spermatids.
  • Spermiogenesis: Spermatids differentiate into mature spermatozoa (sperms).

Sertoli cells provide nourishment and structural support to developing sperms, while Leydig cells secrete testosterone, which regulates spermatogenesis. Below is a simplified diagrammatic representation:


[Diagram: Labeled cross-section of seminiferous tubule showing spermatogonia, spermatocytes, spermatids, spermatozoa, Sertoli cells, and Leydig cells.]
Question 14:
Describe the hormonal regulation of the menstrual cycle in human females. Include the roles of FSH, LH, estrogen, and progesterone.
Answer:

The menstrual cycle is regulated by hormones from the hypothalamus, pituitary, and ovaries:

  • Follicular phase: FSH (Follicle Stimulating Hormone) stimulates follicle development, which secretes estrogen.
  • Ovulation phase: High estrogen triggers LH (Luteinizing Hormone) surge, causing ovulation.
  • Luteal phase: The ruptured follicle forms the corpus luteum, which secretes progesterone to maintain the endometrium.

If fertilization doesn't occur, progesterone levels drop, leading to menstruation. This feedback loop ensures cyclical changes for reproduction.

Question 15:
Describe the process of spermatogenesis in human males with a labeled diagram. Explain the role of hormones involved in this process.
Answer:

Spermatogenesis is the process of formation of spermatozoa (sperm) in the seminiferous tubules of the testes. It involves the following stages:

  • Multiplication Phase: Spermatogonia (diploid stem cells) divide mitotically to produce more spermatogonia.
  • Growth Phase: Some spermatogonia grow in size and form primary spermatocytes (diploid).
  • Maturation Phase: Primary spermatocytes undergo meiosis I to form secondary spermatocytes (haploid), which further divide via meiosis II to form spermatids.
  • Spermiogenesis: Spermatids differentiate into mature spermatozoa by losing excess cytoplasm and developing a tail.

Hormonal Regulation:

  • GnRH (Gonadotropin-Releasing Hormone) from the hypothalamus stimulates the pituitary to release FSH and LH.
  • FSH acts on Sertoli cells to support spermatogenesis.
  • LH stimulates Leydig cells to secrete testosterone, which is essential for sperm production.

(Diagram: Labeled cross-section of seminiferous tubule showing spermatogonia, spermatocytes, spermatids, and spermatozoa.)

Question 16:
Explain the process of spermatogenesis in human males with a labeled diagram. Highlight the role of Sertoli cells and Leydig cells in this process.
Answer:

Spermatogenesis is the process of sperm production in the seminiferous tubules of the testes. It involves the following stages:

  • Multiplication phase: Spermatogonia (diploid stem cells) divide mitotically to produce more spermatogonia.
  • Growth phase: Some spermatogonia grow into primary spermatocytes (diploid).
  • Maturation phase: Primary spermatocytes undergo meiosis I to form secondary spermatocytes (haploid), which then undergo meiosis II to form spermatids (haploid).
  • Spermiogenesis: Spermatids differentiate into mature spermatozoa (sperms).

Sertoli cells provide nourishment and structural support to developing sperms, while Leydig cells secrete testosterone, which regulates spermatogenesis. (Diagram: Labeled seminiferous tubule showing spermatogonia, spermatocytes, spermatids, spermatozoa, Sertoli cells, and Leydig cells.)

Question 17:
Describe the process of spermatogenesis in human males with a labeled diagram. Explain the role of hormones in regulating this process.
Answer:

Spermatogenesis is the process of sperm formation in the seminiferous tubules of the testes. It involves the following stages:

  • Spermatocytogenesis: Primordial germ cells divide mitotically to form spermatogonia, which further divide to form primary spermatocytes. These undergo meiosis I to form secondary spermatocytes, which then undergo meiosis II to form spermatids.
  • Spermiogenesis: Spermatids differentiate into mature spermatozoa (sperms) by developing a head, midpiece, and tail.

Hormonal regulation:

  • GnRH (Gonadotropin-Releasing Hormone): Secreted by the hypothalamus, it stimulates the pituitary to release FSH and LH.
  • FSH (Follicle-Stimulating Hormone): Acts on Sertoli cells to support spermatogenesis and release inhibin (negative feedback).
  • LH (Luteinizing Hormone): Stimulates Leydig cells to produce testosterone, essential for sperm maturation.

Labeled Diagram (Not drawn here but expected in answer):

  • Seminiferous tubule showing spermatogonia, spermatocytes, spermatids, and spermatozoa.
  • Leydig cells (testosterone production) and Sertoli cells (nourishment).

Value-added point: Testosterone also maintains secondary sexual characteristics like muscle growth and voice deepening.

Question 18:
Explain the menstrual cycle in human females, highlighting the hormonal changes and their effects on the ovary and uterus.
Answer:

The menstrual cycle is a 28-day cycle regulated by hormones and involves the ovary (ovarian cycle) and uterus (uterine cycle).

Phases and hormonal changes:

  • Menstrual Phase (Days 1-5): Shedding of the endometrium due to low levels of estrogen and progesterone.
  • Follicular Phase (Days 6-14): FSH stimulates follicle growth in the ovary, leading to estrogen secretion. Estrogen thickens the endometrium.
  • Ovulatory Phase (Day 14): A surge in LH triggers ovulation (release of the ovum from the Graafian follicle).
  • Luteal Phase (Days 15-28): The ruptured follicle forms the corpus luteum, which secretes progesterone to maintain the endometrium. If fertilization doesn't occur, the corpus luteum degenerates, leading to menstruation.

Effects on ovary and uterus:

  • Ovary: Follicle development, ovulation, and corpus luteum formation occur.
  • Uterus: Endometrium prepares for implantation (proliferative and secretory phases) and sheds if pregnancy doesn't occur.
Question 19:
Describe the process of spermatogenesis in humans with a labeled diagram. Explain the role of hormones involved in this process.
Answer:

Spermatogenesis is the process of formation of mature male gametes, called spermatozoa, in the seminiferous tubules of the testes. It involves three main phases:

  • Multiplication Phase: Spermatogonia (diploid stem cells) divide mitotically to produce more spermatogonia.
  • Growth Phase: Some spermatogonia grow in size and become primary spermatocytes (diploid).
  • Maturation Phase: Primary spermatocytes undergo meiosis I to form secondary spermatocytes (haploid), which further divide via meiosis II to produce spermatids (haploid). Spermatids then undergo spermiogenesis to transform into mature spermatozoa.

Hormonal Regulation:

  • GnRH (Gonadotropin-Releasing Hormone): Secreted by the hypothalamus, it stimulates the pituitary to release FSH and LH.
  • FSH (Follicle-Stimulating Hormone): Acts on Sertoli cells to support spermatogenesis.
  • LH (Luteinizing Hormone): Stimulates Leydig cells to secrete testosterone, which is crucial for sperm production.

Diagram: (Draw a labeled diagram of the seminiferous tubule showing spermatogonia, primary spermatocytes, secondary spermatocytes, spermatids, and spermatozoa, along with Sertoli and Leydig cells.)

Value-added Note: Sertoli cells provide nutrition to developing sperm and form the blood-testis barrier, while Leydig cells produce testosterone, highlighting the coordinated role of hormones and cells in spermatogenesis.

Case-based Questions (4 Marks) – with Solutions (CBSE Pattern)

These 4-mark case-based questions assess analytical skills through real-life scenarios. Answers must be based on the case study provided.

Question 1:
A couple is undergoing IVF treatment due to male infertility caused by low sperm motility. The doctor suggests ICSI as a solution. Explain how ICSI differs from conventional IVF and why it is suitable here.
Answer:
Case Deconstruction

In IVF, sperm and egg are mixed externally for fertilization, while ICSI involves direct injection of a single sperm into the egg.

Theoretical Application
  • ICSI bypasses motility issues, ensuring fertilization even with poor sperm movement.
  • Our textbook shows ICSI success rates are higher for male infertility cases.
Critical Evaluation

ICSI is evidence-based, as studies confirm its effectiveness for low sperm motility, unlike standard IVF which relies on natural sperm-egg interaction.

Question 2:
A 16-year-old girl exhibits primary amenorrhea and underdeveloped secondary sexual characteristics. Tests reveal Turner syndrome (45,X). Analyze the hormonal basis of her condition and its reproductive implications.
Answer:
Case Deconstruction

Turner syndrome results from missing X chromosome, causing ovarian dysgenesis and estrogen deficiency.

Theoretical Application
  • Without ovaries, no follicles develop, leading to absent puberty and infertility.
  • We studied that estrogen replacement therapy can induce secondary characteristics but not fertility.
Critical Evaluation

Current data confirms that Turner syndrome patients require lifelong hormonal support due to non-functional gonads, highlighting irreversible reproductive limitations.

Question 3:
During embryo development, a mutation disrupts SRY gene function in a male fetus. Predict the phenotypic outcomes and justify with evidence from sex determination mechanisms.
Answer:
Case Deconstruction

The SRY gene on Y chromosome triggers male development by initiating testes formation.

Theoretical Application
  • Mutation leads to XY females with ovaries (Swyer syndrome), as absent SRY defaults to female pathway.
  • Our textbook shows such cases require hormonal therapy for puberty.
Critical Evaluation

Critical analysis confirms SRY’s master regulatory role, as its loss overrides chromosomal sex, aligning with observed Swyer syndrome phenotypes.

Question 4:
A study links endometriosis to elevated prostaglandin E2 levels. Discuss how this biochemical imbalance causes symptoms like dysmenorrhea and infertility, referencing uterine physiology.
Answer:
Case Deconstruction

Prostaglandin E2 promotes inflammation and abnormal uterine contractions in endometriosis.

Theoretical Application
  • High prostaglandins cause painful cramps (dysmenorrhea) by intensifying myometrial spasms.
  • We studied that inflammation also disrupts implantation, reducing fertility.
Critical Evaluation

Evidence-based research confirms prostaglandin inhibitors alleviate symptoms, validating their pathological role in endometriosis-associated infertility.

Question 5:
A couple is undergoing in vitro fertilization (IVF) due to male infertility caused by low sperm motility. The doctor suggests Intracytoplasmic Sperm Injection (ICSI). Analyze the biological basis of ICSI and its advantages over conventional IVF.
Answer:
Case Deconstruction

ICSI involves injecting a single sperm directly into an egg's cytoplasm, bypassing natural fertilization barriers. This is crucial when sperm motility is impaired.

Theoretical Application
  • ICSI ensures fertilization even with minimal viable sperm
  • Overcomes issues like sperm inability to penetrate zona pellucida
Critical Evaluation

Our textbook shows ICSI has higher success rates (60-70%) than IVF (40-50%) for male infertility. However, it requires specialized equipment and carries slight risks of genetic abnormalities.

Question 6:
During pregnancy, human chorionic gonadotropin (hCG) levels show a specific pattern. Construct a graphical representation of hCG levels across trimesters and explain its correlation with corpus luteum maintenance.
Answer:
Case Deconstruction

hCG peaks at 8-12 weeks then declines. [Diagram: Bell curve showing hCG levels vs weeks]

Theoretical Application
  • hCG rescues corpus luteum from degeneration
  • Sustains progesterone secretion until placenta takes over
Critical Evaluation

We studied how abnormal hCG patterns indicate ectopic pregnancy or miscarriage. The corpus luteum remains active for ~10 weeks due to hCG's LH-like action.

Question 7:
Compare spermatogenesis and oogenesis regarding their duration, gamete production, and hormonal regulation. Present data in a structured format highlighting two key differences.
Answer:
Case Deconstruction
ParameterSpermatogenesisOogenesis
DurationContinuous from pubertyCyclic until menopause
Gametes/cycleMillions1-2
Theoretical Application

FSH stimulates both processes, but testosterone regulates spermatogenesis while estrogen/progesterone control oogenesis.

Critical Evaluation

Our textbook shows primary oocytes remain arrested in prophase I until puberty, unlike spermatogonia which divide continuously.

Question 8:
A study reveals endometriosis affects 10% of reproductive-age women globally. Explain how this condition causes infertility with reference to fallopian tube function and implantation.
Answer:
Case Deconstruction

Endometriosis involves endometrial tissue growth outside uterus, causing inflammation.

Theoretical Application
  • Scarring blocks fallopian tubes, preventing ovum transport
  • Inflammatory cytokines impair embryo implantation
Critical Evaluation

We studied how 30-50% of endometriosis patients face infertility. The ectopic tissue responds to hormonal cycles, creating adhesions that distort pelvic anatomy.

Question 9:
A couple is undergoing IVF (In Vitro Fertilization) due to male infertility caused by low sperm motility. Explain the steps involved in ART (Assisted Reproductive Technology) and how it addresses their issue.
Answer:
Case Deconstruction

In IVF, eggs are retrieved from the female and sperm from the male. Since sperm motility is low, ICSI (Intracytoplasmic Sperm Injection) may be used to directly inject a sperm into the egg.

Theoretical Application
  • Ovarian stimulation via hormones like FSH.
  • Egg retrieval under ultrasound guidance.
  • Sperm collection and processing to isolate viable sperm.
  • Fertilization in lab conditions.
Critical Evaluation

ICSI bypasses motility issues, ensuring fertilization. However, success rates vary (~40%). Ethical concerns include multiple embryo transfers.

Question 10:
A 16-year-old female exhibits primary amenorrhea and underdeveloped secondary sexual characteristics. Analyze possible hormonal imbalances and their effects on reproductive health.
Answer:
Case Deconstruction

Primary amenorrhea suggests hormonal deficiencies, possibly due to hypogonadism or Turner syndrome. Lack of estrogen delays puberty.

Theoretical Application
  • Low FSH/LH levels impair ovarian function.
  • Estrogen deficiency prevents endometrial growth and breast development.
Critical Evaluation

Diagnosis requires karyotyping (e.g., 45,X in Turner’s). Hormone replacement therapy (HRT) can induce puberty but fertility may remain compromised.

Question 11:
During embryogenesis, a teratogen like thalidomide causes limb malformations. Explain how teratogens disrupt development and compare their impact in the first vs. third trimester.
Answer:
Case Deconstruction

Teratogens interfere with organogenesis, especially during the first trimester when limb buds form. Thalidomide inhibits angiogenesis.

Theoretical Application
  • First trimester: Major structural defects (e.g., phocomelia).
  • Third trimester: Functional impairments (e.g., CNS damage).
Critical Evaluation

Our textbook shows thalidomide’s strict regulation now. Critical windows exist; later exposure risks are lower but not absent.

Question 12:
A study links endometriosis to retrograde menstruation. Evaluate this hypothesis and discuss diagnostic methods and treatment options.
Answer:
Case Deconstruction

Retrograde flow deposits endometrial cells outside the uterus, causing inflammation. However, not all women with retrograde flow develop endometriosis.

Theoretical Application
  • Diagnosis: Laparoscopy with biopsy.
  • Treatment: NSAIDs, hormonal therapy (e.g., GnRH agonists), or surgery.
Critical Evaluation

Genetic factors (e.g., WNT4 mutations) may predispose individuals. Hormonal treatments suppress symptoms but aren’t curative.

Question 13:

Rahul and Priya were discussing the process of fertilization in humans. Rahul mentioned that the acrosome reaction is crucial for fertilization, while Priya argued that the cortical reaction is more important. Based on your understanding of human reproduction:

  • Explain the roles of both the acrosome reaction and cortical reaction in fertilization.
  • How do these reactions ensure successful fertilization and prevent polyspermy?
Answer:

The acrosome reaction and cortical reaction are both critical for successful fertilization in humans.

Acrosome Reaction: This occurs when the sperm reaches the zona pellucida of the ovum. The acrosome (a cap-like structure on the sperm head) releases enzymes like hyaluronidase and acrosin, which digest the zona pellucida, allowing the sperm to penetrate and fuse with the ovum's plasma membrane.

Cortical Reaction: After sperm entry, cortical granules in the ovum release enzymes that harden the zona pellucida, forming a fertilization membrane. This prevents other sperm from entering (polyspermy), ensuring only one sperm fertilizes the ovum.

Together, these reactions ensure:
1. Successful sperm-ovum fusion (acrosome reaction).
2. Blockage of additional sperm (cortical reaction), maintaining the diploid chromosome number in the zygote.

Question 14:

During a biology class, students observed a diagram of the male reproductive system. The teacher pointed out the seminiferous tubules and asked:

  • Describe the structure and function of seminiferous tubules.
  • How do Sertoli cells and Leydig cells contribute to sperm production and hormonal regulation?
Answer:

The seminiferous tubules are coiled structures in the testes where spermatogenesis (sperm production) occurs.

Structure: Each tubule is lined with germinal epithelium containing spermatogonia (sperm-forming cells) and Sertoli cells. Surrounding the tubules are Leydig cells (interstitial cells).

Functions:
1. Sertoli Cells: Provide nutrition to developing sperm, secrete inhibin (regulates FSH), and form the blood-testis barrier to protect sperm from immune attacks.
2. Leydig Cells: Secrete testosterone, which stimulates spermatogenesis and maintains male secondary sexual characteristics.

Together, these cells ensure:
- Continuous sperm production (Sertoli cells).
- Hormonal balance (Leydig cells).

Question 15:

A couple visited a fertility clinic due to difficulties in conceiving. The doctor diagnosed the male partner with oligospermia (low sperm count) and suggested Intrauterine Insemination (IUI) as a possible treatment. Explain:

  • The biological basis of IUI.
  • Why it might help in this case.
Answer:

Intrauterine Insemination (IUI) is an assisted reproductive technique where sperm is directly placed into the uterus during ovulation to facilitate fertilization.


Biological Basis: In IUI, sperm is first washed and concentrated in the lab to remove seminal fluid and select highly motile sperm. This processed sperm is then inserted into the uterus via a catheter, bypassing the cervix and increasing the chances of sperm reaching the fallopian tube.


Why it helps in oligospermia: Since the male partner has a low sperm count, IUI concentrates the available sperm and places them closer to the egg, improving the likelihood of fertilization. It also ensures that sperm bypass potential cervical mucus barriers.


Additional Note: IUI is less invasive and more affordable compared to In Vitro Fertilization (IVF), making it a preferred first-line treatment for mild male infertility.

Question 16:

During a school health check-up, a 16-year-old girl was found to have primary amenorrhea (absence of menstruation). The doctor suspected a hormonal imbalance. Answer the following:

  • Name the hormones responsible for regulating the menstrual cycle.
  • How could a deficiency in any of these hormones lead to amenorrhea?
Answer:

The key hormones regulating the menstrual cycle are:

  • Gonadotropin-Releasing Hormone (GnRH) from the hypothalamus
  • Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH) from the pituitary
  • Estrogen and Progesterone from the ovaries

Hormonal Deficiency Effects:


1. Low GnRH/FSH/LH: Insufficient stimulation of ovarian follicles leads to no estrogen production, preventing endometrial thickening and menstruation.


2. Low Estrogen: Without estrogen, the endometrium does not proliferate, and ovulation may not occur, causing amenorrhea.


3. Low Progesterone: Even if ovulation occurs, inadequate progesterone fails to maintain the endometrium, resulting in no menstrual shedding.


Application: Conditions like Polycystic Ovarian Syndrome (PCOS) or hypothalamic dysfunction can disrupt these hormones, leading to amenorrhea.

Question 17:

Rahul and Priya, a married couple, were advised by their doctor to undergo in vitro fertilization (IVF) due to infertility issues. During the procedure, the doctor collected multiple eggs from Priya and sperm from Rahul. The eggs were fertilized in a laboratory, and one of the embryos was implanted into Priya's uterus.

(a) Why is multiple egg collection preferred in IVF?
(b) What is the significance of zona pellucida during fertilization?

Answer:

(a) Multiple egg collection is preferred in IVF to increase the chances of successful fertilization and embryo development.
Ovarian stimulation leads to the production of several eggs, ensuring that even if some eggs fail to fertilize or develop, viable embryos are still available for implantation.

(b) The zona pellucida is a glycoprotein layer surrounding the egg that plays a crucial role in fertilization.
It ensures species-specific sperm binding and prevents polyspermy (entry of multiple sperms) by hardening after the first sperm penetrates, thus maintaining genetic integrity.

Question 18:

During a biology class, students observed a diagram of the male reproductive system. The teacher pointed out the seminiferous tubules and asked:

(a) What is the function of Sertoli cells in the seminiferous tubules?
(b) How does testosterone influence spermatogenesis?

Answer:

(a) Sertoli cells provide nutritional support to developing sperm cells (spermatids) and help in their maturation.
They also secrete inhibin, which regulates FSH (Follicle Stimulating Hormone) secretion from the pituitary gland.

(b) Testosterone, produced by Leydig cells, is essential for:

  • Initiation and maintenance of spermatogenesis
  • Development of secondary sexual characteristics
  • Regulating libido (sex drive) and male fertility

Question 19:
A couple is facing infertility issues due to low sperm motility in the male partner. The doctor suggests Intrauterine Insemination (IUI) as a possible treatment. Explain the process of IUI and how it can help in overcoming infertility in this case.
Answer:

Intrauterine Insemination (IUI) is an assisted reproductive technique where sperm is directly placed into the uterus to facilitate fertilization. Here’s how it works:


1. Sperm Collection: The male partner provides a semen sample, which is then processed in a lab to separate healthy, motile sperm from seminal fluid.
2. Sperm Washing: The sample is 'washed' to remove impurities and concentrate high-quality sperm, improving motility.
3. Insemination: The processed sperm is inserted into the female partner’s uterus using a thin catheter during her ovulation period, increasing the chances of fertilization.


In this case, IUI helps bypass the issue of low sperm motility by placing sperm closer to the fallopian tube, reducing the distance they need to travel. It is a less invasive and cost-effective option compared to In Vitro Fertilization (IVF).

Question 20:
During a prenatal checkup, a pregnant woman is diagnosed with ectopic pregnancy. Explain what ectopic pregnancy is, its potential risks, and why it cannot result in a normal delivery.
Answer:

An ectopic pregnancy occurs when a fertilized egg implants outside the uterus, most commonly in the fallopian tube (tubal pregnancy).


Risks:
1. Rupture: The growing embryo can cause the fallopian tube to burst, leading to severe internal bleeding.
2. Infection: Tissue damage increases the risk of life-threatening infections.
3. Future Fertility Issues: Scarring or removal of the tube may reduce chances of conception.


Why Normal Delivery is Impossible:
The fallopian tube lacks the space and nurturing environment of the uterus. As the embryo grows, it cannot develop properly, and the tube cannot expand like the uterus. This makes it impossible for the pregnancy to reach full term or result in a live birth. Immediate medical intervention (e.g., medication or surgery) is required to prevent complications.

Question 21:
A 35-year-old woman is undergoing in vitro fertilization (IVF) due to blocked fallopian tubes. During the procedure, doctors observe that her oocytes are not maturing properly. Explain the role of gonadotropins in oocyte maturation and how their administration can help in this scenario.
Answer:

In the female reproductive system, gonadotropins (FSH and LH) play a crucial role in oocyte maturation. Follicle-stimulating hormone (FSH) stimulates the growth of ovarian follicles, while luteinizing hormone (LH) triggers ovulation and final maturation of the oocyte.


In IVF, synthetic gonadotropins are administered to:

  • Stimulate multiple follicles to develop, increasing the chances of retrieving mature oocytes.
  • Ensure proper cytoplasmic and nuclear maturation of the oocyte, which is essential for fertilization.

For this woman, exogenous gonadotropins can compensate for inadequate natural hormone levels, promoting follicular growth and oocyte maturation, thereby improving IVF success rates.

Question 22:
A couple is concerned about their newborn showing ambiguous genitalia. Genetic testing reveals the child is 46, XY but has underdeveloped male reproductive structures. Explain how testosterone and Müllerian inhibiting substance (MIS) contribute to normal male reproductive development and what might have gone wrong in this case.
Answer:

In 46, XY embryos, two key hormones direct male reproductive development:

  • Testosterone: Secreted by Leydig cells, it promotes the development of Wolffian ducts into male structures (epididymis, vas deferens).
  • Müllerian inhibiting substance (MIS): Produced by Sertoli cells, it causes regression of Müllerian ducts, preventing female reproductive structures.

In this case, ambiguous genitalia could result from:

  • Defective testosterone synthesis or receptor insensitivity (e.g., androgen insensitivity syndrome).
  • Insufficient MIS production, leading to partial retention of Müllerian structures.

Further hormonal and genetic tests are needed to pinpoint the exact cause, such as mutations in SRY or enzymes in testosterone biosynthesis.

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