Genetic and Hormonal influences on Sexual Development

Question 1

How many pairs of chromosomes does every cell in the human body have?

Answer 1

• 23 (46 individual)
• except gamets

Question 2

Week 0- fertilisation

Answer 2

• sex chromosomes exist as x and y
• if a fertilised egg inherits two x chromosomes it will become female
• if a fertilised egg inherits an x and y chromosome it will become male

Question 3

Week 0-6

Answer 3

• for first 6 weeks following fertilisation males and females devlop identically
• the embryo contains the precursor tissue for making both types of gonads (ovaries/testes)
• cortex of each primordial gonad has potential to devlop into ovaries
• medulla of each primordial gonad has potential to develop into testes
• embryo has two complete sets of internal reproductive ducts

Question 4

Week 0-6: Wolffian system

Answer 4

• precursors of the male reproductive ducts
• seminal vesicles (store sperm)
• vas deferens ( duct from the testes to penis)

Question 5

Week 0-6: Mullerian system

Answer 5

• precursors of the female reproductive ducts
• uterus
• upper vagina
• fallopian tubes

Question 6

Week 6

Answer 6

• SRY (sex determining region Y) gene only found on Y chromosome
• sets in motion a cascade of events which lead to sexual differentiation
• SRY gene produces H-Y antigen which differentiates the foetal testis
• Medulla of primodal gonads develop into testes
• in absence of H-Y antigen the cortical cells of primordial gonads develop into ovaries

Question 7

Week 9-12

Answer 7

• external genitalia visible
• develop from the same precursor tissue in both males and females
• penis and scrotum in males
• labia, clitoris, outer vagina in females
• Androgens produced by testes stimulates external genitalia to become male
• Female external genitalia don’t need to be stimulated by female sex hormones to become female

Question 8

Week 12

Answer 8

In 3rd month of male foetal, testes produce

Mullerian- inhibiting substance
- causes mullerian system to degenerate and testes to descend into the scrotum

Adrogens
- testosterone and dihydrotestorone
- stimulates development of the wolffian system

Question 9

Week 40

Answer 9

• baby boy or girl

Question 10

Genetic issues- Turners syndrome

Answer 10

Week 0
- only one x chromosome present and fully functional

Week 40
- no Y chromosome so testes don’t develop
- two chromosomes required to produce oaries so don’t devlop
- no gonads but devlop normal female internal sex organs and genitalia
- unable to have children as no ovaries

Question 11

Hormonal Issues – Androgen Insensitivity Syndrome

Answer 11

Week 9-
- caused by genetic mutation preventing formation of functioning adrogen receptors
- for male primordial gonards develop into testes but external genitalia insensitive to action of androgens

Week 12-
- testes continue to secrete androgens and mullerian inhibiting sub
- adrogens fail to have masculinising effect so no sex organs
- mullerian inhibiting sub does have defeminising effect so no female organs

Week 40-
- child born appears female
- external genitalia female but no uterus or ovaries
- develops woman’s body at puberty but unable to have children

Question 12

Hormonal Issues – Persistent Müllerian Duct Syndrome

Answer 12

Week 12
- failure to produce mullerian inhibiting sub or absence of receptors for hormone
- androgens have their masculine effect so reproductive system develops
- mullerian inhibiting sub doesn’t have defeminising effect so female internal organs develop

Week 40
- child born with both sets of sex organs
- presence of additional sex organs may interfere with functioning of male sex organs