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Lecture 31 - – Genetic variation is a good thing Sexual...

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BIOL104-04 Principles of Biology I November 12, 2010 Lecture #31 Chapter 11 Sexual reproduction & meiosis
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Meiosis A type of cell division Produces sperm & eggs Daughter cells have half as many chromosomes as parent cell • Diploid ! haploid • 2n ! 1n
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Relationship between chromosomes & chromatids Unreplicated chromosome – Single DNA molecule with its associated proteins • Replicated – Two sister chromatids • Tetrad – Homologous chromosomes that are joined together
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Synapsis 2n 2 A 2 B
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Some species reform nuclear membrane - others do not
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Meosis I ! meosis II Brief interphase No S phase No DNA replication
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1n 1A 1B
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Why sex? Asexual reproduction – Mitosis – Offspring are genetically identical to parents Sexual reproduction – Offspring are genetically unlike their parents – Genetic variation is a good thing
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Unformatted text preview: – Genetic variation is a good thing Sexual reproduction • Produces offspring through the fusion of gametes • Offspring have chromosomal complements that are – Different from each other – Different from the parents How does genetic variation happen? • Crossing over – Exchange of DNA between homologous chromosomes • Independent assortment – Separation & distribution of homologous chromosomes Random assortment of chromosomes on the metaphase plate Independent assortment Mitosis vs. meosis • Mitosis – One round of DNA replication – One division – One cell (2n) ! two cells (2n) • Meosis – One round of DNA replication – Two divisions – One cell (2n) ! four cells (1n) • Movie • In-class activity...
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