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April 29, 2017 at 2:39 am

In the 1960s there was considerable debate

regarding how much genetic variation actually

exists in populations. The common view was

that polymorphic loci are fairly rare. Then, the

development of the technique of gel

electrophoresis allowed biologists to examine

patterns of protein variation across

populations and to quantify genetic variation.

Biologists detected surprisingly large amounts

of genetic variation. In most vertebrate species,

for example, approximately 30 percent of genes

were found to be polymorphic. Studies in the

1970s in humans showed that genetic variation

occurs at approximately the same levels as in

other animal species. The studies in humans

also revealed, famously, that so-called human

races are not real biological groupings. It was

found that there is considerably more genetic

variation within races than between them.

Since then it has been the absence of genetic

variation that is considered anomalous.

Absence of genetic variation in populations

generally suggests that there was a population

bottleneck in the recent history of the group, a

time when the population size became very

small. The result of a population bottleneck is

that all members of the current population are

descended from a small number of individuals,

and therefore have only limited genetic

variation. Genetic variation is expected to build

up over time in these populations as new

mutations appear.