Why are chromosomes considered the source of diversity

Chromosomes can increase genetic diversity by the way they are replicated. Since chromosomes are paired, and sperm and egg cells have only 1 of each pair, few sperm and egg cell wil have identical chromosomes. For humans, with 23 chromosome pairs, the number of possible combination of chromosomes for any child is over 8 million. That means the chance of any 2 siblings (who are not identical twins) having the same chromosomes from both parents is less than 1 in 8 million. Add to that the possibility of chromosomal crossover during the production of sperm or egg cells, and the number of different gene combinations in any child becomes staggering. If a frog, for example, lays a few thousand eggs, chances are that all of them will have different chromosomes within their cells. That may be why natural selection has favored organisms with dozens of pairs of chromosomes. Organisms with lots of chromosomes can maintain a high level of diversity within the population. Since genetically diverse species are more resistant to disease, it is not difficult to understand many different lineages have converged upon the same solution of having dozens of chromosomes.

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