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Integration of the Genotype in Geographic Populations of Drosophila pavani

Danko Brncic
Evolution
Vol. 15, No. 1 (Mar., 1961), pp. 92-97
DOI: 10.2307/2405845
Stable URL: http://www.jstor.org/stable/2405845
Page Count: 6
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Integration of the Genotype in Geographic Populations of Drosophila pavani
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Abstract

Crosses were made between geographic races of D. pavani from localities in Chile and Argentina. All these populations were polymorphic for the gene arrangements in chromosomes II, IV-R, and IV-L, due to the occurrence of inversions. After ten generations, it was observed that the five parental populations which served as controls have maintained the frequencies of the heterozygotes for the inversions around the same values as found in nature. On the other hand, in the nine populations of mixed geographic origin, the frequencies of heterozygotes decreased very significantly. These results suggest that the higher fitness of the inversion heterozygotes depends on the internally balanced gene systems maintained in the inverted segments of the chromosomes. Through a process of natural selection, the systems have become different in each Mendelian population. In the interpopulational hybrids these coadapted gene systems are destroyed, owing to crossing over between chomosomes with the same gene orders. As a consequence, the heterozygotes for inversions no longer possess superior fitness.

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