Sexual Differentiation Flashcards
What is genetic sex?
Chromosomal constitution
XX = female XY = male
Why do we need sex?
Allows genetic material to undergo recombination and allelic assortment to generate variation in populations that allows adaptation to changing selective pressure
What is gonadal sex?
Ovary or testis
Determined by genetic sex of indifferent gonad
What is somatic sex?
External genitalia and phenotype
Determined by gonadal sex through messengers (eg. hormones)
What is the chromosomal constitution of Turner’s syndrome?
XO
What is the chromosomal constitution of superfemale?
XXX
What is the chromosomal constitution of Kleinfelter’s syndrome?
XXY
What is the chromosomal constitution of supermale?
XYY
What is the key factor in establishing the effect of the Y chromosome?
SRY
Sex-determining region of the Y chromosome
How big is the SRY protein?
223 amino acids
Conserved DNA binding domain of 79 amino acids (HMG box)
Binds to both DNA and RNA, affecting their accessibility and stability
What are the effects of SRY?
Affects expression of a number of other genes, eg. SOX9
Causes differentiation of Sertoli cells and Leydig cells
When do the genital ridges form?
During 5th and 6th weeks of development
How do the genital ridges form?
Colonised by primordial germ cells migrating from extraembryonic mesoderm close to yolk sac
What do Sertoli cells do?
Make Mullerian Inhibitory Substance (MIS)
What does MIS do?
Destabilises paramesonephric ducts
What do Leydig cells make?
Testosterone
What does testosterone do?
Stimulates formation of mesonephric ducts
What happens in the absence of MIS?
Female genital ridge develops down default pathway and forms ovary
Mesonephric ducts degenerate
Paramesonephric ducts form oviduct, uterus and upper part of vagina
What do the mesonephric ducts form?
Vas deferens
What is primary hermaphroditism?
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
What is secondary hermaphroditism?
Anomalies of the soma
- CAIS
- Congenital adrenal hyperplasia
- Micropenis
- Hypospadias
What is complete androgen insensitivity syndrome (CAIS)?
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
What is micropenis?
Poorly developed phallus
What is hypospadias?
Urethra opens in ventral penis or in vagina
What is congenital adrenal hyperplasia?
Impaired cortisol secretion leads to increased ACTH levels due to loss of negative feedback
Results in hyperplasia of adrenal cortex
What causes congenital adrenal hyperplasia?
Deficiency of 21-hydroxylase, which breaks down 17-hydroxyprogesterone to 11-deoxycortisol
Cortisol precursors accumulate in excess and are converted to androgens
What are the effects of congenital adrenal hyperplasia?
In utero virilisation of female fetus genitalia
What is gender identity?
An internal state of being - psychological quality
How people think of themselves and identify in terms of sex
What is gender role?
Everything we do that communicates our sex/gender to others
Social gender
At what age does gender identity develop?
By 2 years
What is sexuality?
The part of our emotional and intellectual make up concerned with the erotic
What is paraphilia?
Finding non-human stimuli or behaviours sexually arousing
How does androgen exposure affect sexuality in females?
Greater prevalence of homosexuality in CAH girls
