After Patterson: Evolutie (1981)

After Patterson: Evolutie (1981)

The variation inside a species is preserved because of the fact that in the fertilization half of each chromosome comes from the mother and the other half from the father. Thus the cards are constantly shuffled. However, the cards are still more shuffled because often 'crossing-over' is taking place in the formation of the reproductive cells. During the so-called reduction division (also meiosis: see diagram) parts of the chromatides, originating from the father and the mother, are exchanged. As a consequence traits of the father as well as from the mother occur often in the same chromosome.

Variation inside a species can be increased by mutations. Mutations are sudden changes in the hereditary characteristics. They occur only very seldom, but they can have important consequences when they  take place in the reproductive organs. In this case all kinds of aberrations can occur and sometimes the mutation is lethal. When despite the mutation a normally functioning individual comes into existence, new variation has been added to the species. On top are some examples of mutations: a part of a chromosome can get detached and fill in the gap in the opposite direction. And: a part of a chromosome can change place with a (longer) part of  a second chromosome. The most common mutation is the so-called point mutation in which the chromosome is changed in only one point. Know more? Mutations

Evolution 11

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