Females are Genetic Mosaics

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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 MgtF, FgtM

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

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Congenital Adrenal Hyperplasia (CAH)
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Birds Just Plain Weird

• ZZ males, WZ females
• males preferred?
• Mammalian rules dont seem to fully apply to them
• Gonadal steroids dont appear to be nearly as
  important for sexual differentiation
• Direct genetic effects more pronounced?

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An example of a critical period
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SNB motoneurons are more numerous in male than in
female rats.
FEMALE MALE
400 um
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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!

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Activational Dimorphisms

• posterodorsal medial amygdala 85 larger in
  males
• connected to POA
• Activational effect!

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

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Rough and Tumble Play
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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

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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

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• 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

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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

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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

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