After Pope: Het raadsel van het leven (1986)

After De Beer:Atlas van de evolutie (1966)

This is a drawing of an animal cell. In the nucleus lay the bearers of the hereditary traits, the chromosomes. On the chromosomes the genes are located, which regulate one or more hereditary traits. Outside of the nucleus are many very small bodies, called organelles. A chromosome consists of two coiled strings, called chromatids. One gene consists of two alleles, one on each chromatid. These alleles may be different, though they are part of the same gene. Think of the long pea (A) and the short one (a) of Mendel. A and a are alleles of the length gene of the pea plant. During the formation of the reproductive cells the chromatids diverge and in the end each reproductive cell contains such a single string. When an egg-cell and a sperm-cell fuse, a complete chromosome comes again into existence. Know more? Cell structure

It is very important for natural selection that a population has much variation. Think of the neck of the giraffe. If every individual would have the same genetic characteristics (like it is the case in identical twins), there would be no evolution!

Evolution 10

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