COMPONENTS OF SELECTION IN X CHROMOSOME LINES OF DROSOPHILA MELANOGASTER: SEX RATIO MODIFICATION BY MEIOTIC DRIVE AND VIABILITY SELECTION

摘要

Selection coefficients and segregation parameters have been estimated in 18 randomly chosen lines carrying wild Χ chromosomes on the cn bw genetic background. Each line was studied in replicated crosses of four types, with approximately 100 replications per line per cross. Crosses in which male Χ chromosomes differed exhibited significant sex ratio heterogeneity. Maximum likelihood estimation of segregation parameters revealed two lines in which the proportion of Χ -bearing gametes produced by males was significantly different from Mendelian expectations. These observations suggest that segregation distortion is a common feature of naturally occurring genetic variation. Non-Mendelian segregation has important evolutionary implications.