Introduction to Genetic Analysis 489

Introduction to Genetic Analysis 489 - 44200_15_p481-520...

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488 Chapter 15 Large-Scale Chromosomal Changes gamete from the allopolyploid and an n 1 gamete from the cabbage. The n 2 chromosomes had no pairing part- ners; hence, a normal meiosis could not take place, and the offspring were sterile. Thus, Karpechenko had effec- tively created a new species, with no possibility of gene exchange with either cabbage or radish. He called his new plant Raphanobrassica. In nature, allopolyploidy seems to have been a ma- jor force in the evolution of new plant species. One convincing example is shown by the genus Brassica, as illustrated in Figure 15-9. Here three different parent species have hybridized in all possible pair combina- tions to form new amphidiploid species. Natural poly- ploidy was once viewed as a somewhat rare occurrence, but recent work has shown that it is a recurrent event in many plant species. The use of DNA markers has made it possible to show that polyploids in any popula- tion or area which appear to be the same can have many different parental genotypes as a result of many
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