Plants have multicellular haploid stage. Grasshopper chromosomes (color added)

Plants have multicellular haploid stage.

Grasshopper chromosomes (color added)

Simplification shows cell with diploid 2N=2.

Simplification shows cell with diploid 2N=2.

Simplification shows cell with diploid 2N=2.

In this example 2N=4; the “long” pair and the “short”.

In this example 2N=4; the “long” pair and the “short”.

Remember mitosis?

Cells produce more

identical cells.

Resembles Meiosis II,

when sister chromatids separate and cells divide.

Meiosis I isreduction divisionwhen diploid -->haploid.

Meiosis II is similarto mitosis; doublescell number.

Watch meiosis video,if possible.

How does meiosis generate variation?

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.

Recombinationscrambleschromosomes.

Figure from Hapmap.com

Black Oxford

Canadian StrawberryGoldrush

4 of the 79 apple varieties sold at Fedco seeds in Albion ME

Liberty

Sex is costly.

Abundance of trematode parasites

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host

sSexuality important in escaping parasites.

Errors in meiosis