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Meiosis and Variation

Assexual reproduction ­ Divides by mitosis to form offspring genetically identical to the parent.
Sexual reproduction ­ Production of gametes using meiosis.


Meiosis

Diploid cell with 2 sets of chromosomes divides to form 4 haploid daughter cells (gametes).
When 2 gametes fuse together, they produce a diploid…

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How Meiosis cause Variation

1. Independent assortment ­ Alleles originally from mother mixed with alleles originally from
father.
No. different combinations = 2n, n= haploid no. of chromosomes (23 in humans).
Only if alleles reside on different chromosomes.




2. Crossing over ­ During Prophase 1, chromatids within a bivalent can…

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Alleles which give an advantage become more common in a population over time. Then, if the
environment remains much the same, the alleles in the population should not change much over
successive generations ­ Stabilising selection.

Directional (evolutionary) change = Change in selection pressures means that different alleles are
selected…

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Phylogenetic Species Concept ­ Species is a group of organisms that is geographically separated,
morphologically or behaviourally distinct from other species, even if they can still interbreed to
produce fertile offspring. (Based on evolutionary relationships eg. Common ancestors)


Artifical Selection

The choice of humans of individual organisms from which to…

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