17' Sex

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17. Sex

• Being Male and Female

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Reproduction

• Asexual more efficient (Only 1 sex)
• Low genetic variation
• Sexual prevalent (2 sexes, separate or not)
• High genetic variation
• Need 2 members of the same species

Approaches External fertilization (aquatic
organisms corals) Dont need to find mate,
produce lots of gametes Internal fertilization
(land animals) Need to find mate, fewer
gametes, assure reproduction
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The Origin of Sex
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Primitive Sex Corals
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Primitive Sex Corals

• First reproduction in water
• Sperm and eggs synchronous release
• More sperm than egg
• Sperm swims using a flagella to the egg
• Size difference between gametes
• Corals
• use cycle of the Moon coordinate release
• zygotes free to settle

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Males

• Generalities
• typically larger, stronger, flashier
• Reality
• males may be small, dull, and weak

Definition organism possessing
sperm Characteristics testes organs
producing sperm mammals Y chromosome (XY)
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Females

• Generalities
• typically smaller, weaker, dull
• Reality
• many females are large, strong

Definition organism possessing
eggs Characteristics ovaries organs
producing eggs mammals lack of a Y chromosome
(XX)
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Male or Female
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Discovering the SRY Gene
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Action of the SRY Gene
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SRY Gene

• Sex-determining Region Y
• On the Y chromosome
• Male determination
• Testes development
• Testosterone production
• Leads to male secondary characteristics
• XX can be male if they have SRY gene
• XY can be female if they lack SRY
• 10 to 12 other sex determination genes

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Reproductive Organ Development
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Human sexual differentiation

• Mullerian ducts Female gonads
• Wolffian ducts Male gonads
• Humans default is female
• Each sex starts off as undifferentiated

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External Reproductive Organ Development
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Sexual Characteristics
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Sex and gender
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Sex Chromosome Disorders
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Sex Chromosome Disorders
Klinefelters XXY
Turner Syndrome XO
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Complete Androgen Insensitive Syndrome (CAIS)
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CAIS

• Y chromosome present
• SRY gene functional
• Testis development
• Testosterone production
• Lack testosterone receptors so female development

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Sex and Hormones
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Sex and Hormones

• Testosterone male hormone (testes)
• facial hair, muscle development, deep voice,
  sperm production
• Estrogen female hormone (ovaries)
• breast formation, lower muscle mass, egg
  maturation
• Males and females have both hormones
• ex Testerone in women maintains sex drive
  and bone density
• Estrogen made from Testosterone (1 carbon
  difference)

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Sex Determination Systems
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Crocodile Sex Determination
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Crocodile Sex Determination

• Incubating temperature
• 30oC all female
• 32oC all male
• 31oC 50 female, 50 male

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Wrasse Protogyny
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Protogyny

• Begin life as females
• One dominant male
• One female replaces the dominant male in
  succession
• Harem
• Wrasses, other fish

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Protandry

• Begin life as a male
• Breeding pair
• gt 2 fish
• Dominant fish will become female
• If she dies, the next dominant male changes to
  female
• Crown fish (Nemo)

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• Summary
• Males and females have different purposes
  defined by their gametes
• Development of sexes is dependent on
• genes
• hormones
• environment
• Sex is flexible in some species
• Next time Union
• Reading Hand out Chapter 8 (read it!)