Sources
Mutations are the ultimate source of genetic variation because they alter the order of bases in the nucleotides of DNA. Mutations are likely to be rare and most mutations are neutral or deleterious, but in some instances the new alleles can be favored by natural selection.
Genetic variation can also be produced by the recombination of chromosomes that occurs during sexual reproduction, called independent assortment.
Crossing over and random segregation during meiosis can result in the production of new alleles or new combinations of alleles. Furthermore, random fertilization also contributes to variation.
Variation and recombination can be facilitated by transposable and transposed genetic elements, commonly known as endogenous retroviruses, LINEs, SINEs, etc.
Read more about this topic: Genetic Variation
Famous quotes containing the word sources:
“Even healthy families need outside sources of moral guidance to keep those tensions from imploding—and this means, among other things, a public philosophy of gender equality and concern for child welfare. When instead the larger culture aggrandizes wife beaters, degrades women or nods approvingly at child slappers, the family gets a little more dangerous for everyone, and so, inevitably, does the larger world.”
—Barbara Ehrenreich (20th century)
“I count him a great man who inhabits a higher sphere of thought, into which other men rise with labor and difficulty; he has but to open his eyes to see things in a true light, and in large relations; whilst they must make painful corrections, and keep a vigilant eye on many sources of error.”
—Ralph Waldo Emerson (1803–1882)
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—Anthony Trollope (1815–1882)