Sexual Differentiation

Question 1

What is genetic sex?

Answer 1

Chromosomal constitution

XX = female
XY = male

Question 2

Why do we need sex?

Answer 2

Allows genetic material to undergo recombination and allelic assortment to generate variation in populations that allows adaptation to changing selective pressure

Question 3

What is gonadal sex?

Answer 3

Ovary or testis

Determined by genetic sex of indifferent gonad

Question 4

What is somatic sex?

Answer 4

External genitalia and phenotype

Determined by gonadal sex through messengers (eg. hormones)

Question 5

What is the chromosomal constitution of Turner’s syndrome?

Answer 5

XO

Question 6

What is the chromosomal constitution of superfemale?

Answer 6

XXX

Question 7

What is the chromosomal constitution of Kleinfelter’s syndrome?

Answer 7

XXY

Question 8

What is the chromosomal constitution of supermale?

Answer 8

XYY

Question 9

What is the key factor in establishing the effect of the Y chromosome?

Answer 9

SRY

Sex-determining region of the Y chromosome

Question 10

How big is the SRY protein?

Answer 10

223 amino acids

Conserved DNA binding domain of 79 amino acids (HMG box)

Binds to both DNA and RNA, affecting their accessibility and stability

Question 11

What are the effects of SRY?

Answer 11

Affects expression of a number of other genes, eg. SOX9

Causes differentiation of Sertoli cells and Leydig cells

Question 12

When do the genital ridges form?

Answer 12

During 5th and 6th weeks of development

Question 13

How do the genital ridges form?

Answer 13

Colonised by primordial germ cells migrating from extraembryonic mesoderm close to yolk sac

Question 14

What do Sertoli cells do?

Answer 14

Make Mullerian Inhibitory Substance (MIS)

Question 15

What does MIS do?

Answer 15

Destabilises paramesonephric ducts

Question 16

What do Leydig cells make?

Answer 16

Testosterone

Question 17

What does testosterone do?

Answer 17

Stimulates formation of mesonephric ducts

Question 18

What happens in the absence of MIS?

Answer 18

Female genital ridge develops down default pathway and forms ovary

Mesonephric ducts degenerate

Paramesonephric ducts form oviduct, uterus and upper part of vagina

Question 19

What do the mesonephric ducts form?

Answer 19

Vas deferens

Question 20

What is primary hermaphroditism?

Answer 20

Anomalies of the gonad

Ovary on one side and testis on the other

Mixed ovarian testicular tissue in one or both gonads due to chromosome mosaicism

Question 21

What is secondary hermaphroditism?

Answer 21

Anomalies of the soma

1. CAIS
2. Congenital adrenal hyperplasia
3. Micropenis
4. Hypospadias

Question 22

What is complete androgen insensitivity syndrome (CAIS)?

Answer 22

XY

Testes but female soma

Receptors insensitive to testosterone so lack of male sexual characteristics

No uterus, fallopian tubes or upper vagina due to normal MIS

Question 23

What is micropenis?

Answer 23

Poorly developed phallus

Question 24

What is hypospadias?

Answer 24

Urethra opens in ventral penis or in vagina

Question 25

What is congenital adrenal hyperplasia?

Answer 25

Impaired cortisol secretion leads to increased ACTH levels due to loss of negative feedback Results in hyperplasia of adrenal cortex

Question 26

What causes congenital adrenal hyperplasia?

Answer 26

Deficiency of 21-hydroxylase, which breaks down 17-hydroxyprogesterone to 11-deoxycortisol Cortisol precursors accumulate in excess and are converted to androgens

Question 27

What are the effects of congenital adrenal hyperplasia?

Answer 27

In utero virilisation of female fetus genitalia

Question 28

What is gender identity?

Answer 28

An internal state of being - psychological quality How people think of themselves and identify in terms of sex

Question 29

What is gender role?

Answer 29

Everything we do that communicates our sex/gender to others Social gender

Question 30

At what age does gender identity develop?

Answer 30

By 2 years

Question 31

What is sexuality?

Answer 31

The part of our emotional and intellectual make up concerned with the erotic

Question 32

What is paraphilia?

Answer 32

Finding non-human stimuli or behaviours sexually arousing

Question 33

How does androgen exposure affect sexuality in females?

Answer 33

Greater prevalence of homosexuality in CAH girls