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Allelic Diversity in the Outcrossing Annual Plant Stephanomeria exigua SSP. Carotifera (Compositae)

L. D. Gottlieb
Evolution
Vol. 29, No. 2 (Jun., 1975), pp. 213-225
DOI: 10.2307/2407209
Stable URL: http://www.jstor.org/stable/2407209
Page Count: 13
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Allelic Diversity in the Outcrossing Annual Plant Stephanomeria exigua SSP. Carotifera (Compositae)
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Abstract

Analysis of electrophoretic variation specified by 14 gene loci in 11 populations of the obligately outcrossing, diploid, annual plant Stephanomeria exigua ssp. carotifera, native to California, revealed that all populations possess in common the same gene at six monomorphic loci and 13 alleles in high frequency at eight polymorphic loci. Each population also has a unique selection of 25 low-frequency alleles at the polymorphic loci. The average proportion of the genome heterozygous per individual in the populations ranged from 0.069 to 0.156, with an overall mean of 0.092. The populations were compared with three different types of similarity measures. Nei's genetic identity statistic which utilizes allelic frequencies was calculated; it was shown to be insensitive to the contribution of the low-frequency alleles even though these alleles outnumbered the high-frequency ones by 2:1. The Coefficient of Jaccard was also determined; it compares pairs of populations on the basis of whether they possess the same allele in common. In addition, a new measure called the Complement Index was described that compares the number of non-unique, non-ubiquitous alleles in each population with the total number of such alleles identified in all the populations examined. The Complement Index estimates the extent to which a population is representative of its taxon. One population of ssp. carotifera contained every one of these alleles which suggests that, of all the populations examined, it has the greatest potential for adaptive evolutionary change. Other populations of the subspecies possessed only a third of these alleles. To demonstrate the possible usefulness of the Complement Index in other species, it was also calculated from published data for three animal species. The advantages of emphasizing the number of alleles in a population rather than their frequencies were discussed.

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