Mammalian sex determination, development 3

Question 1

types of sexual dimorphisms

Answer 1

• ultrastructure, biochemistry, molecular mechanisms
• size of specific areas of the brain
• clusters of neurons
• projections and connections between areas
• enzymes, neurotransmitters, receptors

Question 2

mechamisms for brain sexual dimorphisms (3)

Answer 2

• hormone exposure (testosterone, estrogen)
• genetic/chromisomal constitution (XX or XY)
• epigenetic effects (differential methylation of DNA/acetylation of histones)

Question 3

what is the most important influence in brain sexual dimorphisms

Answer 3

steroid/hormone exposure during the perinatal sensitive period –> due to second surge of testosterone production from the testes

Question 4

what do the first and second testosterone surges set

Answer 4

• first: phenotypic sex

- second: brain sex

Question 5

what is sexual dimorphism int he size of different brain nuclei the result of

Answer 5

selective cell death

Question 6

what happens in males v females in selective cell death

Answer 6

• males: steroid exposure rescues/preserves the neurons

- females: steroid exposure results in neuron destruction

Question 7

2 ways testosterone acts on the brain

Answer 7

• directly via androgen receptors

- testosterone aromatized locally (in the brain) to estrogen, which then acts on estrogen receptors

Question 8

2 ways to describe organizational dimorphisms

Answer 8

• developmental

- permanent

Question 9

what are activational dimorphisms

Answer 9

reversible or transient, occur in response to hormone exposure in later life

Question 10

when are behavioral differences set

Answer 10

during sexual differentiation of the brain in the late fetal or neonatal period

Question 11

can female rats be masculinized? if so, how

Answer 11

yes –> single androgen injection in the first few days of life

Question 12

when is mate preference set

Answer 12

developmentally programmed to some extent by exposure to androgen in the perinatal sensitive period, then activated when re-exposed to androgens at puberty

Question 13

sex chromosomes in birds

Answer 13

male: ZZ

- female: ZW

Question 14

3 possibilities for bird sex determination

Answer 14

• dosage system
• dominant W
• cell autonomous sex identity (CASI)

Question 15

what is the dosage system for bird sex determination

Answer 15

• having 2 Z chromosomes sends development down male pathway

- no inactivation, so ZZ males have twice the activity of Z-linked genes than ZW females

Question 16

male bird development

Answer 16

• bilateral testes develop in the absence of estrogenic influence
• normal testicle formation requires both testosterone and MIS
• DMRT1 increases Sox9 (testicle formation), down-regulates female pathway by suppressing FOXL2

Question 17

female bird development

Answer 17

• one copy of DMRT1 –> female pathway not inhibited
• ovarian formation requires aromatase enzyme –> estrogen production (function of FOXL2)
• bipotential gonad differentiates as an ovary, prevents testicular development
• FOXL2 prevents transcription of DMRT1
• only the left ovary develops in most birds (estrogen receptors down-regulated on the right gonad)

Question 18

role for W chromosome in birds

Answer 18

• unknown genes on the W chromosome in ovarian formation

- triploid ZZW chickens start as female, change to male

Question 19

CASI

Answer 19

• cell autonomous sex identity
• sexual phenotype of each cell in the body is determined by the genetic makeup of the cell itself
• half male, half female birds