Sex differences

Question 1

What is the definition of biological sex?

Answer 1

-differences due to sex chromosomes and the cascade of developmental changes that follow in the vast majority of people

Question 2

What are the exceptions of biological sex though?

Answer 2

• 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

Question 3

What is sexual dimorphism?

Answer 3

-differences between sexes in anatomy, physiology, psychology and behaviour

Question 4

What are the different types of hormone action?

Answer 4

• 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)

Question 5

What is the genetic basis of sex differentiation?

Answer 5

• 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

Question 6

What is the gonadal sex differentiation?

Answer 6

• 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

Question 7

What do the testis produce?

Answer 7

• 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)

Question 8

What are the effects of testosterone?

Answer 8

• 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)

Question 9

What is phenotypic sex differentiation?

Answer 9

• 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)

Question 10

What are the further organisational effects of hormones at puberty?

Answer 10

• anterior pituitary releases growth hormone, gonadotropic hormone and adrenocorticotropic hormone
• leads to development of secondary sexual characteristics

Question 11

What are sex differences in behaviour?

Answer 11

-homicide rates: men kill men more frequently, most victims/offenders are young men, pattern is stable across cultures and over time

Question 12

What are sex differences in brain masculinisation?

Answer 12

• 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

Question 13

What are sex differences in sexually dimorphic brain structures?

Answer 13

• 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

Question 14

What are differences in the brain?

Answer 14

• 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