Lecture 19 - The genetics of sex differences in behaviour Flashcards
(38 cards)
Why is the study of sex differences important?
It is relevant to everyone, spans multiple domains of psychology, and most brain and neurodevelopmental disorders exhibit sex biases, such as the female predominance in anorexia and male predominance in autism and ADHD
Define sex differences vs. gender differences
- Sex differences are biological distinctions between males and females, such as chromosomes and hormones
- Gender differences incorporate environmental, cultural, and self-identified influences
On average, what tasks do females outperform males in
- Language tasks (phonological and semantic processing)
- Prose comprehension
- Fine motor coordination
- Perceptual speed
On average, what tasks do males outperform females in?
- Visuospatial working memory
- Motor aiming
- Spatiotemporal processing
- Fluid reasoning (problem solving in novel situations)
Which sex shows greater variability in IQ scores?
Males
How do male and female brains differ structurally?
- Males have larger brains overall and a larger amygdala
- Females have more neuropil (dense dendritic branching)
- Larger corpus callosum
- Hippocampus
- Wernicke’s area
- Orbitofrontal cortex
How do male and female brains differ in wiring?
Male brains tend to show more intrahemispheric (front-to-back) connectivity, whereas female brains show more interhemispheric (left-to-right) connectivity
Which brain region is crucial for regulating sex-specific behaviours like ovulation and bonding?
The hypothalamus, particularly its sexually dimorphic nuclei
Name two key methodological challenges in studying sex differences
1) Small effect sizes with significant overlap between sexes
2) Contextual and task-specific modulation of observed differences
What evidence supports the existence of innate sex differences?
- Sexually dimorphic gene expression occurs in mice before gonadal differentiation
- Rhesus monkey toy preferences mirror human children’s, suggesting non-social factors
Give an example of a disorder with a strong sex bias?
Anorexia nervosa, with significantly higher prevalence in females
What does making refer to in female neurodevelopmental disorders?
The tendency of females to develop compensatory behaviours to hide symptoms, contributing to diagnostic underrecognition (e.g., in ASD)
Who discovered the chromosomal basis of sex determination?
Nettie Stevens, though E.B. Wilson was historically given more credit
What three chromosomal-level differences between males and females?
1) Presence of a Y chromosome in males
2) Two X chromosomes in females vs. one in males
3) Chromosomes in females originate from both parents, wheread males inherit only a maternal X
What are key features of the X chromosome?
- Around 155 million base pairs
- ~1,500 genes, many involved in neurodevelopment and cognition
What are key features of the Y chromosome?
- Around 60 million base pairs
- ~350 pseudogenes and 78 protein-coding genes, most are related to spermatogenesis, but some influence brain function
What is the role od the SRY gene?
The SRY gene initiates testis development, which triggers hormone production that influences brain sexual differentiation
What condition can result from an SRY gene mutation?
Swyer Syndrome: Individuals with XY chromosomes develop as phenotypic females due to non-functional SRY
How does testosterone influence the brain?
Testosterone can be converted to DHT (activating androgen receptors) or estradiol (via aromatase, activating oestrogen receptors), affecting gene expression and neural development
Differentiate organisational and activation effects of hormones
- Organisational effects occur early (prenatal/perinatal) and shape long-term brain structure
- Activational effects occur later (e.g., puberty) and modulate behaviour
What does the Extreme Male Brain theory suggest?
Autism Spectrum Disorder (ASD) reflects an exaggeration of traits more typical in males, such as systemising rather than empathising
What evidence supports prenatal testosterone’s link to ASD traits?
Studies using 2D:4D digit ratios and Q-CHAT scores show small but suggestive correlations, though sample sizes remain limited
What genes are commonly linked to autistic traits?
Genes involved in:
- Steroid biosynthesis (e.g., CYP17A1)
- Neural growth (e.g., NRXN1)
- Social-emotional processing (e.g., OXTR)
Can genes affect brain sexual differentiation directly, independent of hormones?
Yes. Gynandromorphic zebra finches display hemispheric brain differences alligned with genetic sex despite equal hormone exposure
