sex differences

What is biological sex and what are its exceptions?

Biological sex:

• Based on sex chromosomes (XX vs XY)

• Leads to cascade of developmental changes

Exceptions:

• Other genotypes (Turner XO, Klinefelter XXY)

• Atypical development (androgen insensitivity)

• Medical interventions (hormone therapy, reassignment)

What are the two types of hormone action?

Organizational Effects:

• Affects tissue differentiation and development

• Permanent changes

• Occurs during development

Activational Effects:

• Occurs in fully developed organism

• Transient changes

• May depend on prior organizational effects

How is genetic sex determined?

• Human cells have 46 chromosomes (23 pairs)

• 22 pairs of autosomes

• 1 pair of sex chromosomes

• Sex determined by father's sperm (X or Y)

• Gametes are haploid (one copy of each chromosome)

• Y chromosome presence determines male development

How does gonadal differentiation work?

• Starts with undifferentiated primordial gonads

• Ovaries don't produce significant hormones during development

• Testes produce androgens and AMH

• Testosterone is primary androgen

• Produced by Leydig cells in testes

• Sertoli cells produce AMH

What is the sex-determining cascade?

1. Genotypic sex determines gonadal sex

2. Gonadal sex determines phenotypic sex

3. Sex steroids exposure during critical periods causes:

   • Body differentiation

   • Brain differentiation

   • Behavioral differences

What are sex differences in aggressive behavior?

• Men show more severe violence to men

• Most victims and offenders are young men

• Pattern stable across cultures and time

• Suggests testosterone involvement

• Environmental and social factors also important

How do female hormones affect behavior?

Mammalian Estrous Cycle:

• Cyclic gonadotropin secretion (FSH, LH)

• Triggered by GnRH surge

• Most mammals only sexually active during estrus

Human Menstrual Cycle:

• Fertility window limited

• Behavioral and physiological changes throughout cycle

• Less strict behavioral regulation than other mammals

What are sex differences in the brain?

Physical Differences:

• Male brains 10-15% heavier

• Female brains less lateralized

• Some structures sexually dimorphic

Examples:

• Song control region in birds (larger in males)

• SDN-POA in rat hypothalamus

• Effects often established during development