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Why is genetic diversity important to the survival of a species?

Do the founding species of islands show a lack of genetic diversity?

  • I read somewhere if there was less than a certain number of sexual pairs of a species (like 100)  it would die out.  Seems island species would have this problem, especially non-flying ones.  I guess there might be waves of immigration to help genetic diversity.  Is there something in the DNA of remote island species that shows this lack of diversity?

  • Answer:

    Yes, islands are famous for low genetic diversity and one consequence of that, founder effects. A small group gets to an island, and they are reproductively isolated from others of their species. If one of the founders had a deleterious allele, it becomes concentrated in the population, and in time many people will be homozygous for that allele and have an abnormality. One such example is the Pacific atoll Pingelap, which Oliver Sacks wrote about in Island of the Colorblind. On this island, 5-10% of the population exhibits the inability to see any type of color (achromatopsia) combined with blindness in full light conditions. These people have a mutation in the gene CNGB3, which is necessary for cone cell function. In a normal, large population,such a mutation would arise once, and it would either be randomly lost in the next generation or only seen in a handful of people; it would be unlikely to be present homozygously. However, everyone on a small, reproductively isolated island is slightly inbred, since there are not many choices for mates. So many people will carry the mutation, and many people will carry two copies of the mutation and have the disease.

Melinda T. Owens at Quora Visit the source

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Good answers here already. Adding just a bit, for good luck: Diversity in a population arises both out of the recombination of genes during sexual reproduction and also random mutations.  Natural selection favors mutations that increase fitness.  In large populations and/or those with high fecundity, there are lots of opportunities for mutations to occur and for natural selection to act on them, but in smaller populations, there are far fewer.  This can lead to a process called genetic drift. The best way to explain genetic drift is using a big bag of red and green m&m's.  Say you had 1000 candies in the bag, 500 of each.  If you pulled out, say, 800 of them, you'd get a pretty even mix of red and green.  But if you pulled out 20, your chances of getting a representative sample are much lower.  You could wind up with, say, 14 red and 6 green, and if those m&m's got together and had little m&m's babies, there would be a lot more red ones than green ones.  Genes work in much the same way in small populations, and yes, this is endemic to island populations.

Christine Condo

There's a difference between a population that starts with a small number of people (e.g. after migration to an island) and a population that has been reduced to a small number. IIRC, it's estimated that if a species has dwindled to less than 50 individuals, the likelihood of extinction is so high that it's considered not worth the effort to try to revive the species. But a small population migrating to a new area might well thrive, if the checks on population size that existed in their previous home (i.e. predators, competitors for food, etc.) don't exist in the new area.

Dave Williams

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