Sex differences in behaviour and cognition Flashcards
what are types of sex differences?
- Genetic or chromosomal sex
- Gonadal sex
- Internal reproductive system
- External reproductive system
- Pubertal sex changes
- Hormonal sex
- Brain sex
- Behavioural and ‘cognitive’ sex
- Sexual identity
genetic or chromosomal sex
- XX = female
- XY = male
- sex chromosome determined by the father
sexual differentiation
- organisational effects of sex hormones produced by fetal gondas
- permanent alterations in body or CNS induced by a hormone at a ‘critical’ period in development
- activational effects of sex hormones also produced by gonads
- hormon effects that occur in the fully developed organism; depend on previous effects
development of male sex organs
- SYR region on the Y chromosome codes for testis-determining factor (a transcription factor) that binds to DNA in cells of undifferentiated gonads and causes them to become testes
- Testes produces hormones that have a defeminising (anti-mullerian hormone) and masculinising (androgen) effects
what is testes-determining factor?
- 230 amino-acid long protein coded for by SYR region of Y chromosome
- Transcription factor binding DNA induces conformational changes that enable transcription
- point mutations can prevent development if testes (and hence of internal and external male sex organs) in XY individuals
what is anti-mullerian hormone and how does it work?
- a peptide secreted by the fetal testes that has defeminising effects
- it inhibits the development of the Mullerian system (precursor of female internal sex organs) by acting on Mullerian hormone receptors in the cell system
what are Androgens: testosterone and dilhdrotestosterone and hwo do they work?
Two androgens are the primary causes of masculinisation during early development:
- Testosterone acts on androgen receptors in cells of the Wolffian system and stimulates its development into male internal sex organs.
- Dihydrotestosterone, produced from testosterone by 5alpha reductase, acts on androgen receptors in the primordial external genitals (with higher affinity than testosterone) and is critical to stimulate their development into male genitals.
what factors determine the development of female sex organs
- primordial sex organs develop into female sex organs
- in the absence of testis-determining factor primordial gonads develop into ovaries
- In the absence of androgens produced by testes, internal and external sex organs develop into female organs (without any other hormonal influence necessary)
what is XY sex reversal? Werner et al, 1995
Point mutations in the SRY region of the Y chromosome result in female sex organs in XY individuals
what is Androgen insensitivity syndrome?
A condition caused by congenital lack of functioning androgen receptors; in a person with XY sex chromosomes, causes development of a female with testes but no internal sex organs.
what is Turner’s syndrome?
The presence of only one sex chromosome (an X chromosome) results in lack of ovaries but otherwise normal female sex organs and genitalia
what is Persistent Mullerian duct syndrome?
In an XY individual, congenital lack of anti-Mullerian hormone causes the development of both male and female internal sex organs
what is sexual maturation (puberty)?
- primary sex characteristics (gonads, internal and external sex organs) are present at birth, secondary sex characteristics (enlarged breasts, widened hip, facial hair, deep voice) and sexual maturity are not developed until puberty.
- Puberty is triggered by hypothalamic secretion of gonadotropin-releasing hormone (GnRH)
- secondary sex characteristics, control of reproductive functions and sexual behaviour (and other behaviour)
- axillary and pubic hair in females are stimulated by testosterone produced by cortex of adrenal glands
what is the organisational hypothesis? Young et al
- exposing male female rats and guinea pigs to androgen in utero during critical periods altered their sexual behaviour
- Young et al proposed that early androgens, similar to their effects on sex organs, organise the devloping CNS in a masculine way, so make female behaviour less likiley (determinsation) and male behaviours more likely (masculinisation)
what are natural and behavioural sex differences?
- Since publication of the organisational hypothesis, many sex differences in the CNS have been reported in many vertebrates, including humans.
- In line with the organisational hypothesis many neural sexual dimorphisms in rodents have been demonstrated to depend on organising effects of androgens during critical developmental periods
- Other neural sexual dimorphisms have been demonstrated to depend on both organising and activating effects of androgens, and yet others only involve activating (and reversible) effects during adulthood.
- There is evidence that neural sexual dimorphisms contribute substantially to sex differences in behaviour (especially reproductive behaviour), often in conjunction with activating effects of sex hormones on sexually dimorphic neural systems.
- There are also many instances of neural sexual dimorphisms described without obvious behavioural correlates and of behavioural sex differences (often produced by hormone effects) for which no clear neural substrates have yet been identified.
- There is also evidence for an interaction between environmental and hormonal influences on neural and behavioural sexual dimorphisms – so ‘nature’ and ‘nurture’ seem to interact.
