Sex differences Flashcards
What is the definition of biological sex?
-differences due to sex chromosomes and the cascade of developmental changes that follow in the vast majority of people
What are the exceptions of biological sex though?
- people with other genotypes
- people with XX/XY genotype but atypical development often due to mutations
- people who have undergone medical procedures to alter sex/gender phenotype
What is sexual dimorphism?
-differences between sexes in anatomy, physiology, psychology and behaviour
What are the different types 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 effects of hormones, transient (level of hormone changes and there’s a physiological and behavioural response to that change)
What is the genetic basis of sex differentiation?
- sex is genetically determined
- diploid human cells contain 46 chromosomes (23 matched pairs): 22 pairs of autosomes, 1 pair of sex chromosomes
- gametes are haploid (1 copy, so produce 2 X or 1 of each)
- gametes fuse to create diploid offspring
- sex is determined by the males gametes
What is the gonadal sex differentiation?
- at 6 weeks after conception the primordial gonads of XX and XY individuals are identical
- if no Y is present the cortex of the primordial gonad develops into an ovary, if present the medulla of the primordial gonad develops into a testis (these changes occur because of the SRY gene)
- if no SRY gene so no SRY protein the gonads develop into an ovary
What do the testis produce?
- various androgens (including testosterone) that lead to the masculinisation of many other tissues
- produces anti-Mullerian hormone (AMH) that masculinises internal genitalia (Mullerian ducts regress)
What are the effects of testosterone?
- steroid hormone
- primary androgen
- synthesised by Leydig cells in testes
- sertoli cells produce AMH
- when it’s produced, the enzyme of 5-alpha-reductase is possessed which leads to dihydrotestosterone (DHT) which governs development of male genitalia (DHT promotes masculinisation of external genitalia)
What is phenotypic sex differentiation?
- genotypic sex determines gonadal sex, gonadal sex determines phenotypic sex
- differential exposure to sex steroids causes sexual differentiation of the body, brain and behaviour (permanent effects)
What are the further organisational effects of hormones at puberty?
- anterior pituitary releases growth hormone, gonadotropic hormone and adrenocorticotropic hormone
- leads to development of secondary sexual characteristics
What are sex differences in behaviour?
-homicide rates: men kill men more frequently, most victims/offenders are young men, pattern is stable across cultures and over time
What are sex differences in brain masculinisation?
- female guinea pigs treated with testosterone when pregnant produce defeminised, masculinised daughters with male-typical behaviour
- female rhesus macaques given testosterone as new-borns show male-typical behaviour as adults: pursuit and mounting of other females, pelvic thrusting, post-ejaculatory behaviours, preference for female partners
What are sex differences in sexually dimorphic brain structures?
- song control region in zebra finches: 5-6 times larger in males than in females, gets bigger in females given testosterone as hatchlings
- rat hypothalamus: sexually dimorphic nucleus of pre-optic area (SDN-POA): smaller in males castrated at birth, bigger in females given testosterone at birth, no effect of castration/testosterone treatment in adulthood
What are differences in the brain?
- on average male brains are 120-160g heavier, also heavier relative to brain size
- female brains less strongly lateralised, anatomical lateralisation appears more marked in males
- parts of corpus callosum are bigger in right-handed men than left
