Sex differences Flashcards
Lecture 9B (13 cards)
Sex, gender and sexuality
- Gender - what we identify personally as, sociocultural construct
- Sexual orientation - sexual attraction
- Biological sex is differences due to sex chromosomes and the cascade of developmental changes in majority of people (some exceptions)
sexual dimorphism
- differences between sexes in anatomy, physiology, psychology and behaviour
- for many traits, there’s more variation within each sex than between them
sex differences
- type of hormone action
- sexual differentiation - genetic, gonadal, phenotypical
- sex differences in behaviour
- sex differences in the brain
testosterone
- knowledge of the involvement of testes and sex hormones in behaviour comes traditionally from animal husbandry
- has been used across the world for centuries to avoid aggression and reproduction
- Eunuchs - practice in the ancient world to control behaviours in humans, during development only and effect is not related to amount of testosterone, minimal amount is enough to reinstate male-typical sexual behaviour
type of hormone action
- organisational effects - effects on tissue differentiation and development, permanent
- activational effects - effects that occur in fully developed organism, may depend on prior exposure to organisational effect of hormones, transient
- sexual differentiation in mammals depends on organisational effects of hormones during development
genetic basis of sex differentiation
- sex is genetically determined
- diploid human cells contain 46 chromosomes - 23 pairs of autosomes, 1 pair of sex chromosomes
- biological sex is determined randomly by the type of male’s gametes
- gametes are haploid, just one copy of each chromosome
- gametes fuse to create diploid offspring
- biological sex is determined by the presence or absense of the Y chromosome in the sperm cell
- undifferentiated ‘primordial’ gonads, not yet ovaries or testes until 6 weeks
- during early embryonic development, no SRY (sex determining region Y gene) gene = no SRY protein = ovary which is the default, if SRY gene, SRY protein = testes, sets off chain of events that results in either female or male
Gonadal sex differentiation
Ovaries:
1. during early embryonic development ovary does not produce significant amounts of steroid hormones during embryonic development
2. each part of the body develops according to its own intrinsic programme
Testis:
1. produce various androgens including testosterone, masculinises many other tissues
2. produces anti-mullerian hormone - masculinised internal genitalia
Testosterone:
1. steroid hormone, fat soluble, passes readily through cell membrane
2. synthesised by Leydig cells in testes
sex determining cascade
- XX - no SRY gene - ovaries - feminisation
- XY - SRY gene - SRY protein - testes - masculinising hormones - masculinisation
phenotypic sex differentiation
- differential exposure to sex steroids during critical periods of development causes sexual differentiation of the body, brain and behaviour
- permanent effects
- testosterone - 5 alpha reductase - dihydrotestosterone
- no testosterone - 5AR - no DHT
- effect of hormone present in development promotes later development of anatomical or behavioural characteristics typical of males
- AMH - internal genitalia
- DHT - external
- further organisation effects of hormones at puberty - testosterone from testes, hormones released by anterior pituitary leads to development of secondary sexual characteristics
sex differences in behaviour
Aggressive behaviour:
1. homicide rates 68% males attack males, 20% males attack female, 10% female attacks males, 2% females attack females
2. most victims and offenders are young men, stable pattern across cultures and time
3. suggests involvement of testosterone in male-male aggressive behaviour
Mammalian oestrous cycle:
1. cyclic patterns of gonadotropin secretion present only in females, prompted by surge in GnRH above tonic levels
2. pro-oestrus - follicular development and ovulation
3. oestrus - recptive period during which fertilisation is mosy likely to lead to pregnancy
4. most female mammals are only sexually active during oestrus phase
Human menstrual cycle:
1. fertile window - conception only likely if sperm is present in the reproductive tract when ovulation takes place
2. behavioural and physiological changes
3. not much evidence of differences in sexual activity across menstrual phases
Premenstrual dysphoric disorder:
1. severe premenstrual disorder affecting 3-8% of menstruating women
2. occurs within 1 week before period starts
3. mood swings, depression, anxiety, physical symptoms
4. treatments of hormone therapy, antidepressants
reproductive behaviour in humans
- masters and johnson - detailed lab observations of physiology and behaviour during intercourse, 4 stage response (Excitement, plateau, orgasm, resolution)
- similarities in both males and females
sexually dimorphic brain structures
- song control region in zebra finches - 5-6 times larger in males than females, females given testosterone gets bigger
- rat hypothalamus sexually dimorphic nucleus of preoptic area - smaller in males castrated at birth, bigger in females given testosterone at birth, no effect in adulthood
Sex differences in human brain
- brain size - on average male brains are 120-160g bigger
- brain lateralisation - female brain less strongly lateralised in terms of various functions than male brains, anatomical lateralisation of the cerebral hemispheres appears to be more marked in males
