Founder Principle OR Founder Effect

When a few individuals or a small group migrate from a main population, only a limited portion of the parental gene pool is carried away.

In the small migrant group, some genes may be absent or occur in such low frequency that they may be easily lost. 

The unique frequency of genes that arise in population derived from small bands of colonizers or “founders”, has been called the founder effect or founder principle. 

This principle was proposed in 1956 by Harvard evolutionist, Ernst Mayr. 

The founder principle essentially emphasizes the conditions or circumstances that support the operation of Sewall Wright’s genetic drift. 

Example

North American Indian tribes, for the most part, lack the gene IB that governs type B blood. However, in Asia, the ancestral home of the American Indians, the IB gene is widespread. 

The ancestral population of Mongoloids that migrated across the Bering Strait to North America might have been very small.

 Accordingly, the possibility exists that none of the prehistoric immigrants happened to be blood group B. It is also likely that a few individuals of the migrant band did carry the IB gene but they failed to leave descendants.

Evolutionary geneticists interpret this peculiar feature in terms of genetic drift. 

Most of the North American Indians possess only blood group O, or stated another way, contain only the blood allele i.

With few exceptions, the North American Indian tribes have lost not only blood group allele IB but also the allele that controls type A blood (IA). 

The loss of both alleles, IA and IB, by sheer chance perhaps defies credibility. 

Indeed, many modern students of evolution are convinced that some strong selective force led to the rapid elimination of the IAand IB genes in the American Indian populations.

 If this is true, it would provide an impressive example of the action of natural selection in modifying the frequencies of the genes in a population.

Reference

CELL BIOLOGY,GENETICS,MOLECULAR BIOLOGY, EVOLUTION AND ECOLOGY.

VERMA  AND AGARAL