Females are Genetic Mosaics

1. Females are Genetic Mosaics • Female mammals “turn off” one entire X chromosome in each cell early in development =XCI • Not perfect up to 20% of X genes escape XCI, so some sex chromosome genes M>F, F>M

2. 5-alpha-reductase deficiency • Males are usually infertile due in part to genital malformation = hypospadias

3. Congenital Adrenal Hyperplasia (CAH)

4. Birds – Just Plain Weird • ZZ males, WZ females • males “preferred”? • Mammalian rules don’t seem to fully apply to them • Gonadal steroids don’t appear to be nearly as important for sexual differentiation • Direct genetic effects more pronounced?

5. An example of a critical period

8. SNB motoneurons are more numerous in male than in female rats. FEMALE MALE 400 um

10. Activational effects on the SNB • Testosterone maintains: • Muscle size • Motoneuron soma size • Motoneuron dendritic length • Synaptic density on Motoneurons • Function of the reflexes • Most of these happen because of AR in muscle!

11. Activational Dimorphisms • posterodorsal medial amygdala – 85% larger in males • connected to POA • Activational effect!

12. Keep in mind – much overlap between sexes in most behaviors • more variation within each sex, than between sexes

13. Rough and Tumble Play

14. Non-Sexual Sex Differences in Humans • Numerous differences observed cross-culturally • A. Sensory Systems • 1. Olfaction • women better at identifying odors at all ages • women sense musk 1000x more easily than men • begins at puberty, is estrogen-dependent • periovulatory and early pregnancy – better sensitivity • menstruating and late pregnancy – worse sensitivity • 2. Taste • women higher sensitivity than men • better at identifying tastes, and discriminating them • begins at puberty, highest at pregnancy/ovulation • in rats, due to lack of perinatal androgen and then • activated by estrogens

15. Non-Sexual Sex Differences in Humans • Numerous cognitive differences observed cross-culturally • A. Sensory Systems • 3. Audition • women more sensitive than men • hear tones at lower thresholds • particularly true for higher pitches • tolerance for loudness of white noise less • women have louder evoked otoacoustic emissions • cochlea makes faint echo-like noises • sex difference at birth, organized by hormones • females with male twin more male-like • gay or bisexual women more male-like

16. 4. Vision • men higher visual acuity than women • see objects more clearly at further distances • women tolerate higher light intensity than men • women undergo dark adaptation faster • visuospatial abilities better in men • not known how hormones affect

17. Non-Sexual Sex Differences in Humans • B. Lateralization of Cognitive Function • cerebral hemispheres somewhat specialized • example – right side best at spatial processing, • left side best at verbal processing • females less lateralized than males • hemisphere size more similar in women • sex difference in corpus callosum • females’ cognitive function more distributed • men slower and more mistakes in responding to • auditory stimuli entering left ear • women equally good for stimuli at either ear/eye • stroke on left side affects speech more in males • stroke on right side affects vision more in males

18. Non-Sexual Sex Differences in Humans • C. Verbal and Mathematical Skills • no sex difference in IQ • however, small sex differences in some skills • females better at: • verbal skills • language comp., acquisition, spelling, grammar • perceptual skills • fine motor skills • mathematical calculations • males better at: • interception of projectile objects • quantitative tasks • visuospatial ability • maps, directional sense, mazes, math reasoning

19. But Hormonally Based? Almost all of these sex difference arise after puberty, so activational hormone basis? Not that simple – recall organizational limits on activational effects CAH women – maybe enhanced visuospatial ability suggest organizational effects do happen mathematical reasoning difference exists prior to puberty (but gender roles and early environment effects) Again, recall that individual differences are more important than sex differences in this regard!

20. Source of Sex Differences in Cognitive Ability Brain Structure e.g. superior temporal cortex and Broca’s area are 20% larger in females BUT use can affect structure: Brain activity fMRI patterns differ between sexes when asked to do same task