Genetic Variation and Selection Response in Model Breeding Populations of Brassica rapa Following a Diversity Bottleneck
William H Briggs 1* and Irwin L Goldman 1
1 University of Wisconsin-Madison
* To whom correspondence should be addressed. E-mail: whbriggs{at}wisc.edu.
Submitted on January 14, 2005
Revised on April 21, 2005
Accepted on 3 September 2005
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Abstract |
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Domestication and breeding share a common feature of population bottlenecks followed by significant genetic gain. To date, no crop models have been developed to investigate the evolution of genetic variance, selection response, and population diversity following bottlenecks. We developed a model artificial selection system in the laboratory using rapid-cycling Brassica rapa. Responses to ten cycles of recurrent selection for cotyledon size were compared across a broad population founded with two hundred individuals, three bottleneck populations initiated with two individuals each, and unselected controls. Additive genetic variance and heritability were significantly larger in the bottleneck populations prior to selection and this corresponded to a heightened response of bottleneck populations during the first three cycles. However, the overall response was ultimately greater and more sustained in the broad population. AFLP marker analyses revealed the pattern and extent of population subdivision were unaffected by a bottleneck even though the diversity retained in a selection population was significantly limited. Rapid gain in bottlenecked populations, particularly in the short term, may offer an explanation for why domesticators and breeders have realized significant selection progress over relatively short time periods.
Key Words:
genetic diversity, plant breeding, population bottleneck, recurrent selection
