How can genetic drift affect a population

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Biology Evolution Genetic Drift. Kate M. Sep 12, Explanation: Genetic drift decreases genetic diversity within a population. Related questions Why is genetic drift undesirable in a population? How does genetic drift differ from natural selection? We will return to this theme after introducing the concept of metapopulations. Mycosphaerella graminicola causes Septoria tritici leaf blotch on wheat. McDonald and colleagues used restriction fragment length polymorphism RFLP markers to determine the genetic structure of this pathogen worldwide and found that all populations collected from different geographic locations had similar frequencies of common alleles except the populations collected from Australia and Mexico Zhan et al.

The Australian and Mexican populations had significantly lower gene diversity shown in Table 1 , fewer alleles at each locus, fixed alleles at several RFLP loci, and the gene frequencies were significantly different from populations at other locations.

In Australia, this is probably due to a founder effect whereby only a relatively small number of individuals arrived on this continent with the introduction of modern agriculture.

This nursery is located far away from wheat production areas hence, it has a limited potential for influx of natural inoculum and was inoculated with a limited number of strains, presenting a clear example of genetic drift due to a small founding population and continued geographical isolation.

In contrast, the Israeli population had the highest level of gene diversity, consistent with the hypothesis that the Middle East is the center of origin for this pathogen. Table 1. Populations from Mexico and Australia show low gene diversity consistent with founder effects while the Israeli population shows highest gene diversity consistent with the center of origin.

An extreme example of genetic drift due to a bottleneck is the population of the Phytophthora infestans pathogen that causes late blight of potatoes. It appears that the original global pandemic was caused by a single clone that escaped out of Mexico and into North America, was introduced into Europe causing the Irish potato famine and then was transported around the world as a result of human commerce Goodwin et al.

Stripe rust of wheat Puccina striiformis in Australia shows evidence for a single founder event. Only one race was found in , corresponding to a race found in Europe, suggesting that Europe was the source of the introduction. Since the original introduction, mutations have created new pathotypes in the single introduced genetic background Steele et al. Chestnut blight Cryphonectria parasitica in North America also shows some characteristics of a founder population as it has much less genetic diversity than populations in Asia.

It appears that the center of diversity and possible center of origin is in Japan Milgroom et al. Go to References. Next Section. Log In Bookstore Join Renew. It looks like your browser does not have JavaScript enabled. Email Facebook Twitter. Effects of genetic drift. Through sampling error, genetic drift can cause populations to lose genetic variation. Decreasing variation Imagine that our random draws from the marble bag produced the following pattern: , , , , , , , , , … Why did we keep drawing ?

The impact on small populations The marble-drawing scenario also illustrates why drift affects small populations more.