Sex differences I Flashcards
What are organisational effects of sex hormones?
Permanent alterations in the body induced by a hormone at a critical period in development, occurring before birth.
What are activational effects of sex hormones?
Hormone effects that occur in the fully developed organism after birth which depend on previous organisation effects.
What is the first step in the process of the development of male sex organs?
- A transcription factor called testis-determining factor is coded for by the SRY region on the Y chromosome. This protein binds to DNA in cells of undifferentiated gonads and causes them to become testes.
What is the second step in the process of the development of male sex organs?
- Testes produce the anti-Mullerian hormone that has defeminising effects and androgens that have masculinising effects.
What is the Mullerian system?
A precursor of female internal sex organs
What is the Anti-Mullerian hormone and what does it do in the masculinization process?
It is a peptide secreted by the foetal testes that act on that inhibits the development of the Mullerian system.
Which two androgens are the primary causes of masculinization during early development?
testosterone and dihydrotestosterone
Which androgens are responsible for development of the internal male sex organs?
testosterone
Which androgens are responsible for the development of the external male genitals?
dihydrotestosterone
Testosterone acts on androgen receptors in the cells of which system?
Wolffian system- the precursor of the male internal sex organs
In the absence of the testes-determining factor, what happens?
Gonads develop into ovaries
By default, primordial sex organs develop into..?
female sex organs
The genetic sex of a human foetus is determined by…
The father’s sperm
The prenatal development of female internal sex organs requires…
no hormones at all
In XY sex reversal, point mutations in the SRY region on the Y chromosome, results in what?
Female sex organs in XY individuals
Androgen insensitivity syndrome is a congenital condition in individuals with XY chromosomes. What phenotype does this produce?
A lack of androgen receptors causes development of a female however, the active anti-Mullerian system means that no internal sex organs are produced.
Females with Turner’s syndrome have only one X chromosome and this results in…
lack of ovaries
Lack of anti-Mullerian hormone in XY individuals causes the development of both male and female internal sex organs. What is the name of this syndrome?
Persistent Mullerian duct syndrome/ intersex
Gonadotropic-releasing hormone(GnRH) is secreted by which structure in the brain?
hypothalamus
GnRH acts on which gland in both males and females?
pituitary gland
In males, GnRH causes the pituitary gland to secrete gonadotropic hormones (FSH and LH) which then causes what to happen?
the testis produce testosterone and male puberty occurs
In females, GnRH causes the pituitary gland to secrete gonadotropic hormones (FSH and LH) which then causes what to happen?
the ovaries produce estradiol and female puberty occurs.
What is sexual dimorphism?
It is a condition where the two sexes of a species exhibit differentiating characteristics beyond the different sex organs.
William Young’s Organisational hypothesis aims to explain sex differences in brain and behaviour. What did he propose?
He proposed that early androgens, as well as affecting sex organs, also organise and develop the CNS in a masculine way causing masculinisation.
What findings did William Young base his Organisational hypothesis on?
Experiments on female rats and guinea pigs, found that exposing them to androgens in utero during critical periods altered their adult sexual behaviour.
Neural sexual dimorphisms have been demonstrated to depend on what?
Organisational effects of androgens alone, Activating effects of androgens alone and both. Environmental influences also may play a role
Many masculinising effects of testosterone were found to be mediated by oestrogen in which type of animals?
rodents
Following on from the findings that oestrogen also has a masculinising effect on the brain and behaviour in rodents, what hypothesis was proposed?
Aromatisation hypothesis
What does the Aromatisation hypothesis propose happens during masculinisation?
testosterone is converted to oestrogen by an enzyme called aromatase before it acts on oestrogen receptors in the nuclei of some CNS cells.
In response to the Aromatisation hypothesis, which hypothesis was introduced to account for the feminising effects of oestrogen?
Protection hypothesis
What does the Protection hypothesis state?
The brains of developing rodents are protected from the masculinising effects of oestrogen by an oestrogen-binding protein called alpha-fetoprotein in the blood. This protein prevents testosterone from binding to oestrogen receptor and exerting it’s masculinsing effects.
