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Interaction Between Inversion Polymorphisms of Two Chromosome Pairs in the Grasshopper, Moraba scurra

R. C. Lewontin and M. J. D. White
Evolution
Vol. 14, No. 1 (Mar., 1960), pp. 116-129
DOI: 10.2307/2405927
Stable URL: http://www.jstor.org/stable/2405927
Page Count: 14
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Interaction Between Inversion Polymorphisms of Two Chromosome Pairs in the Grasshopper, Moraba scurra
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Abstract

All the data currently available on the frequencies of inversions in chromosomes CD and EF of the grasshopper Moraba scurra, in certain populations in southern New South Wales, indicate an equilibrium condition in which the Blundell arrangement for chromosome CD and the Standard arrangement for chromosome EF predominate. Estimates of viability based on deviations of adult frequencies from binomial-square proportion show that there are epistatic interactions between the non-allelic arrangements in determining genotypic fitness. From these estimates adaptive surfaces have been constructed which reveal that each population sampled is at a "saddle" or minimax point of the adaptive surface. The possible reasons for the apparent equilibrium condition of the populations at such an unstable point have been examined, and it is tentatively hypothesized that the equilibrium is maintained by a combination of gene frequency-dependent selection and yearly fluctuations in the physical factors of the environment.

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