How does crossing over affect evolution?

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Mary K. Share
Aug 25, 2015

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Crossing over allows genetic variants on the same chromosome to evolve independently, which greatly increases an organism's evolutionary potential.

Explanation:

If there were no crossing over, all genetic variants on a chromosome would be inherited as a block. Image a chromosome copy which contains a good variant--let's say, flu resistance--at one gene, and a bad variant--let's say, tapeworm susceptibility--at a different gene. Without crossing over, the population has to choose between flu and tapeworms. Crossing over can produce a chromosome with the good variant and without the bad one, allowing the population to move toward a better solution. This speeds up the rate of adaptation.

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Jul 28, 2014

Here's what happens: you may already know that evolution is driven by selection for or against genes. We inherit genes on chromosomes that form in haploid cells.

In order for this to occur, cells such as sperm or egg have to divide during meiosis. In meiosis the sets of identical chromosomes line up and genes are able to exchange places at their locus ( the place where the gene is located on the chromosome). See the diagram:
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This ability to switch affects the outcome of the gamete and as such evolution. In most examples of genetics we can inherit either dominant or recessive traits from our parents. Genes determine the proteins that will function in the organism as well as other tasks.

When genes cross over there may be a better chance of it being inherited due to selective pressure. If this is the case, the gene may be active, influence a protein that may be favorable, and the organism may benefit.

It may go the other way. This is the idea of negative or positive selective pressure. See the example of the fruit flies getting different characteristics.
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If the gene provides different outcomes the organism may evolve in that direction or it could die. In other words the gene was beneficial or not, an if so evolution results.

You could consider the finches of Darwin's study. The original population had all the genes but due selective pressure and breeding, and probably crossing over, different finches resulted, each suited for different food (seed) types.

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