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Asexual Reproduction
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-use mitosis
-progeny are identical to parent cells
-does not involve fertilization
-little/no genetic diversity
-useful when env does not change
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Sexual Reproduction
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-involves meiosis & fertilization
-brings together chromosomes from 2 diff parents to generate unique offspring
-generates genetic diversity very quickly- every generation
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Genetic diversity is the raw material that fuels evolution, which sexual reproduction generates more diversity?
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-No genetic process generates diversity more quickly than sexual reproduction
-Limited to genetic variation present in individuals of species due to rare occurence or mutations.
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Beneficial mutations?
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Even more rare-but advantageous to preserve in population, esp. in various combinations
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Life cycles of seually-reproducing organisms- basic pattern:
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-Haploid (1 copy of chromo.) cells or org's alternate w/diploid (2 copies of chromo. (homologous)) cells or org's
-org's vary in prominence of haploid/diploid phases in life cycle
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Gametes
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(eggs and sperm) contain half the complement of chromo. found in other cells produced by gametogenesis
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Fusion of gametes is called....
& what does it create?
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fertilization or syngamy
-the zygote, which contains two copies of each chromo
(3 types of sexual life cycles)
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Meiosis
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-2 successie divisions, but only 1 DNA replication
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Meiosis I
Synapsis
Genetic recombination
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(reduction division)
-separates the 2 versions of each chromo.
-Synapsis-pairing of homologous chromo during prophase I
-Genetic recombo- exchange of genetic material during prophase I (crossing over)
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Meiosis II
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(separation division)
-separates the 2 sister chromatids (from DNA replication) of each chromo into daughter cells
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What does meiosis reduce the chromo num too?
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-It halves the number of chromo- diploid parent cell results in haploid daughter cells
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Animal Cell Meiosis
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.....
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Interphase I
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DNA replicates, centrosome with centriols replicate, cell prepares for divison
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MEIOSIS I
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....
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Early Prophase I / Mid Prophase I / Late Prophase I
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Early Prophase I
Dna condenses into chromosomes
Nuclear envelope breaks down
Mid Prophase I
Mitotic spindle forms (kinetechore MT/fibers, polar MT, astral MT)
Centrosomes migrate to opp cell poles
Synapsis of homologous chromosomes
Late Prophase I
Crossing over-exchange genetic material occurs
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