Biological Science 2/e

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Plants have multicellular haploid stage.
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Grasshopper chromosomes (color added)
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Simplification shows cell with diploid 2N2.
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Simplification shows cell with diploid 2N2.
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Simplification shows cell with diploid 2N2.
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In this example 2N4 the long pair and the
short.
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In this example 2N4 the long pair and the
short.
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Remember mitosis? Cells produce more identical
cells. Resembles Meiosis II, when sister
chromatids separate and cells divide.
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Meiosis I is reduction division when diploid
--gt haploid. Meiosis II is similar to
mitosis doubles cell number.
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Watch meiosis video,if possible.
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How does meiosis generate variation?
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Even without crossing over, meiosis generates
variation. 2N combinations of maternal and
paternal chromosomes. Humans 223 8.4
million Recombination dramatically increases
possibilities. In humans, about 50 chiasmata in
meiosis I. Almost limitless variety of
re-shuffling.
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Recombination scrambles chromosomes.
Figure from Hapmap.com
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4 of the 79 apple varieties sold at Fedco seeds
in Albion ME
Canadian Strawberry
Goldrush
Liberty
Black Oxford
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Sex is costly.
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Sexuality important in escaping parasites.
Predominance of sex in snail hosts
Abundance of trematode parasites
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Errors in meiosis
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