The Nature of Linkage Variation with Age in Inversion Heterozygotes of Drosophila Melanogaster

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Abstract
When al2 Cy lt3 L4 sp2/S Pfd females with inversions involving the regions of Cy and L4 were mated to lt3 males an age effect on crossing over was observed, with the majority of crossovers coming from eggs laid during the first 5 days of adult life. Statistical examination of the data by families for the regions Cy-lt3 and lt3-L4 indicated a clustering of the crossovers into groups of 2 or more rather than a random distr. as would be expected from meiotic crossing over. Two or more crossovers in one region were accompanied by at least one crossover in the adjacent region in 6 out of 8 families. The occurrence of multiple crossovers was sporadic and contributed to the non-random distr. The clustering of crossovers may be due to crossing over in an oogonial cell which was the common ancestor for a number of eggs, or to a weakening of a specific region of a chromosome in a gonial cell, which could influence the location of crossing over in a number of meiotic cells. It is suggested that recombination data for chromosome maps should be collected from the later periods of egg-laying and from large numbers of females in order to measure the variability present.