Sexual Differences in Males and Females

Question 1

State the secondary characteristics of males. (4)

Answer 1

1. deepening of voice
2. development of sexual hair (pubic, axillary, facial)
3. descent of testis into scrotum from inguinal region
4. growth of penis

Question 2

State the secondary characteristics of females. (4)

Answer 2

1. thelarche - development of breasts
2. menarche (first period)
3. development of sexual hair (axillary, pubic)
4. widening of hips

Question 3

State the genetic determinant (factor) of males. State the gene that encodes this factor and cells stimulated by factor.

Answer 3

factor = TDF (testis determining factor)
- encoded by SRY gene in Y chromosome
* nuclear transcription factor (acts in nucleus)
* expressed in gonad before divergence of ovary/testicular development
* cells stimulated - sertoli + leydig cells

Question 4

State the PRO-MALE and PRO-FEMALE factors

Answer 4

PRO-MALE: SRY, SOX9
PRO-FEMALE: FOXL2, WNT4, FST

Question 5

Explain how the external male genitalia and internal male genitalia develop starting from the genotype of the individual.

hint: use big ass flow chart

Answer 5

1. males have XY genotype
2. presence of Y chromosome - encodes SRY gene –> development of testis
3. Testis stimulates development of SERTOLI CELLS which produce ANTI-MULLERIAN HORMONE which prevents development of MULLERIAN DUCT and prevents development of uterus
4. Testis stimulates development of LEYDIG CELLS which produces TESTOSTERONE which stimulates development of INTERNAL MALE GENITALIA (vas deferens, seminal vesicle, epididymis)
5. TESTOSTERONE is converted to DHT (dihydrotestosterone) by 5a-REDUCTASE which stimulates development of EXTERNAL MALE GENITALIA (penis, penile urethra, scrotum, prostate)

Question 6

Explain how the external female genitalia and internal female genitalia develop starting from the genotype of the individual.

hint: use big ass flow chart

Answer 6

1. females have XX/XO genotype
2. absence of Y chromosome - no SRY gene –> no TDF encoded
3. Absence of TDF results in absence of SERTOLI CELLS which results in absence of ANTI-MULLERIAN HORMONE –> absence of regression of MULLERIAN DUCT –> internal female genitalia
4. Absence of TDF results in absence of LEYDIG CELLS which results in absence of TESTOSTERONE resulting in WOLFFIAN DUCT REGRESSION resulting in no internal male genitalia formed
5. Estradiol is produced by ovaries –> external female genitalia

Question 7

Recap: State the external and internal male and female genitalia and the hormones that direct their development.

Answer 7

MALE:
- External genitalia - penis, penile urethra, scrotum, prostate (not external) <– DHT
- Internal genitalia - vas deferens, seminal vesicles, epididymis <– TESTOSTERONE

FEMALE:
- External genitalia - clitoris, labia majora, labia minora, lower 2/3 vagina <– ESTRADIOL
- Internal genitalia - uterus, upper 1/3 vagina, fallopian tubes <– NO MULLERIAN-INHIBITING SUBSTANCES

Question 8

State the embryological derivatives of parts of the genitalia.

Answer 8