THE ORGANIZATION OF GENETIC VARIATION FOR RECOMBINATION IN DROSOPHILA MELANOGASTER

ABSTRACT The amount and form of natural genetic variation for recombination were studied in six lines for which second chromosomes were extracted from a natural population of Drosophila melanogaster. Multiply marked second, Χ and third chromosomes were used to score recombination. Recombination in the second chromosomes varied in both amount and distribution. These second chromosomes caused variation in the amount and distribution of crossing over in the Χ chromosome and also caused variation in the amount, but not the distribution, of crossing over in the third chromosome. The total amount of crossing over on a chromosome varied by 12-14%. One small region varied twofold; other regions varied by 16-38%. Lines with less crossing over on one chromosome generally had less crossing over on other chromosomes, the opposite of the standard interchromosomal effect. These results show that modifiers of recombination can affect more than one chromosome, and that the variation exists for fine-scale response to selection on recombination.

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Inherited Differences in Crossing Over and Gene Conversion Frequencies Between Wild Strains of Sordaria fimicola From “Evolution Canyon”

Genetics ◽

10.1093/genetics/159.4.1573 ◽

2001 ◽

Vol 159 (4) ◽

pp. 1573-1593

Author(s):

Muhammad Saleem ◽

Bernard C Lamb ◽

Eviatar Nevo

Keyword(s):

Genetic Variation ◽

Gene Conversion ◽

Spontaneous Mutation ◽

Crossing Over ◽

Natural Genetic Variation ◽

Evolution Canyon ◽

Wild Strains ◽

Sordaria Fimicola ◽

First And Second Generation ◽

Consistent Direction

Abstract Recombination generates new combinations of existing genetic variation and therefore may be important in adaptation and evolution. We investigated whether there was natural genetic variation for recombination frequencies and whether any such variation was environment related and possibly adaptive. Crossing over and gene conversion frequencies often differed significantly in a consistent direction between wild strains of the fungus Sordaria fimicola isolated from a harsher or a milder microscale environment in “Evolution Canyon,” Israel. First- and second-generation descendants from selfing the original strains from the harsher, more variable, south-facing slope had higher frequencies of crossing over in locus-centromere intervals and of gene conversion than those from the lusher north-facing slopes. There were some significant differences between strains within slopes, but these were less marked than between slopes. Such inherited variation could provide a basis for natural selection for optimum recombination frequencies in each environment. There were no significant differences in meiotic hybrid DNA correction frequencies between strains from the different slopes. The conversion analysis was made using only conversions to wild type, because estimations of conversion to mutant were affected by a high frequency of spontaneous mutation. There was no polarized segregation of chromosomes at meiosis I or of chromatids at meiosis II.

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