Lecture 16 - Genetics of Sex Differences in Behaviour

Question 1

Why study sex differences?

Answer 1

• Relevant to all
• Relevant to many areas of psychology
• Most brain disorders show some sort of sex bias

Question 2

Define sex differences:

Answer 2

• Variations in biology between men and women

Question 3

Describe gender differences:

Answer 3

• Differences between men and women in terms of biology and self-representation as shaped by the environment

Question 4

What are notable sex differences?

Answer 4

• Language acquisition: female vocab is 2x larger
• Physical aggression/behavioural disinhibition
• Sexual preferences

Question 5

When do females outperform males?

Answer 5

• Memory for phonological and semantic
• Prose production and comprehension
• Fine motor skills assessment
• Assessing perceptual speed
• More cross talk among hemispheres e.g unilateral stroke = females are better at coping

Question 6

When do males outperform females?

Answer 6

• Motor skills in aiming
• Transformations in visuospatial working memory
• Fluid reasoning
• Spatiotemporal responding

Question 7

What about IQ?

Answer 7

• Average is roughly the same but men have more variability

Question 8

Sex differences in brain structure:

Answer 8

• Male brain bigger from 2 weeks but female brain has more developed neuropil
• Females mature more rapidly
• Females have a larger Wernicke’s area, orbitofrontal cortex, corpus collosum, hippocampus.
• Men have larger amygdala, fronto-medial cortex
• Male brains are wired back to front
• Female brains wired left to right
• Can be seen through fMRI

Question 9

What are differences in brain structure related to?

Answer 9

• Regulate sex-specific physiology/behaviour e.g ovulation

Question 10

What are key issues in sex differences research?

Answer 10

• Small effect sizes with lots of overlap
• Temporal specificity = children level out vocab after a certain age but females develop it faster
• Effects of menstrual cycle
• Differences in test performance modulated by context = telling people you are testing by gender affects results
• Studies in model organisms use males
• Difference in brain structure do not predict behavioural differences
• Differences are not deficiencies
• Most studies are performed in WEIRD populations
• Differences supported by evidence can be used for prejudice
• Differences may arise due to social conditioning or selection bias

Question 11

Why are sex differences more nature than nurture?

Answer 11

• Differences in genes and brain
• Differences in male/female toys when given to Rhesus monkeys and other animals.

Question 12

What are the GENERAL sex differences in neurodevelopmental and psych disorders?

Answer 12

• Prevalence e.g more females have anorexia
• Age-at-onset
• Disorder subtypes and co-morbidity
• Clinical course e.g males are more likely to get more addictive disorders
• Underlying neurobiology e.g ADHD & Autism
• Response to therapy.

Question 13

How are different rates of diagnosis affecting the sexes?

Answer 13

• More overt and disruptive behaviours
• Closer conformation to diagnostic form
• More abstract obsessions
• More effective masking strategies in females

Question 14

What are mechanisms underlying sexual differentiation of the brain

Answer 14

• Due to chromosome complement
• Males have a Y chromosome
• Females have two X
• Which X do they get from which parent

Question 15

Describe the difference between X and Y chromosome?

Answer 15

• X is larger
• Contains genes involved in neurodevelopment
• Y is smaller and contains pseudo genes
• Most genes are involved in sperm production - some expressed in brain

Question 16

What is SRY and what does it influence?

Answer 16

• Influences brain development indirectly via gonadal hormones
• Identified as testis-determining factor in the early 1990s
• XY, XXY, XXXY subjects = male
• Sry-transgenic XX mice sterile males
• Translocation of part of Y chromosome containing SRY to X chromosomes can cause XX male syndrome
• Rare XY females with mutations of SRY (Swyer syndrome)

Question 17

What does the SRY gene do?

Answer 17

• Causes would be ovaries to turn into testes
• Releases androgens: highly concentrated in sexually dimorphic development

Question 18

How do androgens affect masculinisation?

Answer 18

• Critical pre/perinatal periods
• Genital virilization
• Gender determination
• Increase under 4-6 mo. Postnatally
• Later life e.g puberty

Question 19

What is the extreme male brain theory?

Answer 19

• Males and females differ with regard to systemising and empathising behaviours
• Individuals with autism have more systemising behaviours than empathising
• Suggested people with autism have been exposed to high levels of androgens in their life
• Tested that in utero testosterone correlates to later male/autistic traits
• Indirect methods: finger length e.g ring finger longer than index
  People with autism have genes changes with X

Question 20

What experiments took place in guinea pigs?

Answer 20

• Female GPs and gave them testosterone and acting more aggressive
• Male GPs and removed testes and became more passive

Question 21

What do Gynandromorphic birds show?

Answer 21

• Left side = testicle, right = ovary
• Every cell in body is covered by same hormones

Question 22

How does SRY influence brain function?

Answer 22

• Highly expressed in dopaminergic activity
• Many male-biased disorders exhibit dopaminergic disorders
• Other Y-linked genes may confer risk in males

Question 23

What does higher expression of X-linked genes do?

Answer 23

• One X is switched off to ensure equal activity with males
• 20% of all linked genes are more highly expressed in female brain as they are expressed from both X chromosomes
• Could confer protection against disorders

Question 24

What is the parental origin of the X chromosome?

Answer 24

• Turner syndrome inherit single chromosome from mum/dad
• Compare brain structure
• The maternal one is more likely to show deficits in social cognition
• Protective effect of paternal X = better at social processes