November30 - Biology 442 Developmental Biology Lecture 10...

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Biology 442 Developmental Biology Lecture 10 Sex Determination
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Lecture outline I. Sex determination is not always permanent or binary II. Primary versus secondary sex determination - Cells that undergo primary sex determination - Primary sex determination switches (chromosomes, environment) III. Primary sex determination in: - Flies - Mammals IV. Secondary sex determination (mammals) - Hormonal regulation of sexual phenotype V. Sexual dimorphisms of the brain
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Learning objectives for this class Define primary versus secondary sex determination Name sex determination switches in different organisms Compare and contrast primary sex determination in flies versus humans Describe how hormones control the development of secondary sex characteristics Compare and contrast brain sex determination versus sex determination in other somatic tissues.
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I. Sex determination is not always permanent or binary Sex determination is the process by which an organism acquires sexual characteristics. Sex determination is not always permanent Example: Tropical clownfish: - All clownfish are born male - A clownfish group consists of a dominant male and female and 0-4 juvenile males - When the female dies, the dominant male becomes the dominant female and one of the juveniles becomes the dominant male www.reefteach.com.au/Clown_Fish.htm
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Sex is not always binary Sexual phenotypes in plainfin midshipman fish ( Porichthys notatus ) Type I Male: - Large body size - Vocalize (“hum”) to attract mate and defend territory - Excavate and defend nest - Cares for eggs and hatchlings - Mates by courting and attracting females Female: - Small body size - Only short vocalizations - No nesting or care of young - Lays eggs in nests of Type I males Type II Male: - Small body size - Only short vocalizations - No nesting or care of young - Huge testis - Two mating strategies: ”sneak spawning”--enters nest of Type I male and fertilizes eggs “satellite spawning” - sperm deposited outside the nest and fanned sperm into nest
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II. Primary vs. secondary sex determination Primary sex determination: a tissue or cell directly assesses its sex (cell autonomous). 1. Cells that undergo primary sex determination: - Flies: all cells of the body - Mammals: gonadal cells 2. Primary sex determination is determined by chromosomes and sometimes by the environment Secondary sex determination: a tissue or cell receives information about sexual identity from another tissue (non-cell autonomous): somatic cells in mammals.
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Most Drosophila cells undergo primary sex determination Sex is determined within each individual Drosophila cell by the ratio of X chromosomes to autosomes. This mode of primary sex determination is demonstrated by the generation of Gynandromorphic flies.
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