Sex Differences

Question 1

BIOLOGICAL SEX

Answer 1

• differences due to sex chromosomes (XX VS XY)/developmental changes cascade that follow in vast majority of people
• exceptions include:
  1. other genotypes (ie. Turner (XO)/Klinefelter syndrome (XXY))
  2. XX/XY genotype BUT atypical development oft due to mutations (ie. androgen insensitivity syndrome/5alpha-reductase deficiency)
  3. medical procedures to alter sex/gender phenotype (ie. hormone therapy/gender reassignment surgery)

Question 2

SEXUAL DIMORPHISM

Answer 2

• difs between sexes in anatomy/physiology/psychology/beh

- women/men dif (psych/beh) on average; +1 variation within each sex than between

Question 3

TYPES OF HORMONE ACTION

Answer 3

• organisational effects = tissue differentiation/development effects; permanent
• activational effects = effects occurring in fully developed organism; may depend on prior organisation hormone effect exposure; transient
• mammal sexual differentiation depends on organisational hormone effects during development

Question 4

SEX DIFFERENTIATION GENETIC BASIS

Answer 4

• sex = genetically determined
• diploid human cells contain 46 chromosomes (23 matched pairs; 22 autosomes, 1 pair sex chromosome)
• gametes fuse to create diploid offspring
• bio sex determined randomly by male gamete’s (sperm) type/presence or absence of Y chromosome
• SRY (sex-determining region Y) gene (aka TDF (testis-determining factor gene)

Question 5

GONADAL SEX DIFFERENCES

Answer 5

• 6 weeks post conception, primordial gonads of XX/XY = identical (undifferentiated)
• XX (F) = w/o Y chromosome/SRY gene/SRY protein, primordial gonad cortex develops into ovary
• XY (M) = under Y chromosome/SRY gene/SRY protein influence, primordial gonad medulla develops into testes

Question 6

EARLY EMBRYONIC GONDAL DEVELOPMENT

Answer 6

OVARY
- doesn’t produce sig steroid hormone amount during embryonic development
- each body part develops according to its own intrinsic programme
TESTIS
- various androgens inc. testosterone masculinise many other tissues (ie. brain effects)
- AMH (anti-Mullerian hormone) masculinises internal genitalia (aka. Mullerian regression factor)

Question 7

TESTOSTERONE

Answer 7

• steroid hormone (fat soluble/passes readily via cell membrane)
• primary androgen
• synthesised by Leydig cells in testes
• Sertoli cells produce AMH
• testosterone + 5 alpha reductase = DHT (dihydrotestosterone)

Question 8

SEX-DETERMINING CASCADE

Answer 8

genotypic sex (XX/XY) -> gonadal sex (ovaries/testes) -> phenotypic sex (feminisation/masculinisation)

Question 9

PHENOTYPIC SEX DIFFERENTIATION

Answer 9

• permanent effects
• genotypic sex determines gonadal sex
• gonadal sex determines phenotypic sex
• differential exposure to sex steroids during critical development periods (ie. foetal development/puberty) causes:
  1. bodily sexual differentiation
  2. brain/beh sexual differentiation

Question 10

MASCULINISATION & DE-FEMINISATION

Answer 10

• hormone effect present early in development promotes later anatomical/beh characteristic development typical of males
• AMH -> internal genitalia
• DHT -> external genitalia
• testosterone -> rest of body (incl. brain)

Question 11

PUBERTY

Answer 11

• further organisational hormone effects on puberty:
• anterior pituitary releases GH/gonadotropic hormone/adrenocorticotropic hormone ->
• secondary sexual characteristics development

Question 12

HUMAN SEXUAL BEHAVIOUR

Answer 12

MASTERS & JOHNSON (1966)

• detailed lab obvs of physiology/beh during intercourse = excitement/plateau/orgasm
• assigned partners
• 4 physiological sexual stimulation response stages = excitement/plateau/orgasm/resoltion
• male/female similarities

Question 13

HOMICIDE RATES

Answer 13

DALY & WILSON (1988)

• US reports
• 96.7% same-sex homicides = m/m
• both offenders/victims = primarily men; stable pattern across cultures/time
• men severe violence to men > women severe violence on women

Question 14

BRAIN MASCULINISATION

Answer 14

• female guinea pigs treated w/testosterone when pregnant produce defeminised/masculinised daughters w/male-typical beh
• female rhesus macaques treated w/testosterone as newborns show male-typical beh as adults:
  1. pursuit/mounting of females
  2. pelvic thrusting
  3. post-ejaculatory behs
  4. female partners pref

Question 15

SEXUALLY DIMORPHIC BRAIN STRUCTURES

Answer 15

• song control region in zebra finches; 5-6 xlarger in males > females; gets bigger in females given testosterone as hatchlings
• rat hypothalamus; (SDN-POA) pre-optic area sexually dimorphic nucleus; smaller in males castrated at birth; bigger in females given testosterone at birth; no effect of castration/testosterone treatment in adulthood

Question 16

BRAIN SIZE

Answer 16

• on average male brains = 120-160g (10-15%) heavier
• also heavier relative to body size
• dif present at birth despite equal body weights
• could mean:
  1. female brains > efficient?
  2. extra weight due to extra neurons OR supporting cells/water?
  3. more necessarily better?
  4. correlation between brain weight/performance in specific domains?

Question 17

BRAIN LATERISATION

Answer 17

• female brains less strongly lateralised w/respect to various functions than male brains
• anatomical cerebral hemispheres lateralisation appears more marked in males

Question 18

HEMISPHERE CONNECTIONS

Answer 18

• corpus callosum parts bigger in right-handed > left-handed men; no such pattern for women
• posterior portion (splenium) perhaps more bulbous in women > men

Question 19

SUMMARY

Answer 19

• hormones = organisational effects on tissue differentiation/development/activational effects on beh
• genotypic sex (XX/XY) determines gonadal sex which via sex steroid production determines phenotypic sex
• SRY production in genotypic males initiates processes cascade; masculinise/de-feminise developing embryo
• further organisational hormone effects at puberty -> secondary sexual characteristics development
• men/women more similar > dif BUT some sex difs in body/brain/beh
• sex difs functional significance in brain = still unclear