RECOMBINATION INCREASE DUE TO HETEROLOGOUS INVERSIONS AND THE RELATION TO CYTOLOGICAL LENGTH

Publisher Website
Google Scholar
Abstract
Crossing over in the extreme left end of the X chromosomes in y w5la/spl females was measured for four inversion types: those without inversions, those heterozygous for the Curly inversions of II, those heterozygous for the Payne inversions of HI, and those heterozygous for both Curly and Payne inversions. The inversion chromosomes taken separately increased crossing over 2-3 times the value without inversions; together, 3 1/2 to over 6 times; younger females giving the higher ratios. For each inversion type, crossover values for y-w5la and for w51a-spl were increased equally within the limits of error; this was true both of first cultures (age of mothers 2-6 days) and of subcultures (age of mothers 7-11 days). Since the cytological lengths of these two subregions are known to be as 20-1, there was a marked difference in the response of the subregions to the heterologous inversions with respect to the increase in recombination per unit of cytological length. Coefficients of crossing over for the subregions remained approximately in the ratio of 1-20. Thus the short distal yellow-split region, a region of marked general increase in the presence of the inversions, can still be separated into subregions acting in a constant relationship to one another as regards their capacity to increase per unit of length. The suggestion is made that the mechanism producing the increases is different from that which results in the discrepancies between linkage and cytological maps.