A CHROMOSOMAL ANALYSIS OF EGG PRODUCTION AND ABDOMINAL CHAETA NUMBER INDROSOPHILA MELANOGASTER

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Abstract
A marked-inversion-outcross technique was used to produce the 81 possible combinations of entire chromosomes (genotypes) resulting from crosses of two isogenic lines. Two metric traits, egg production during the 6th, 7th and 8th day and the number of chaeta on the fourth and fifth abdominal segments, were measured. Heterogeneity of within-genotype variance was found for both traits. There is some evidence of increasing variance with increasing homozygosity, bur it is not conclusive.Egg production is influenced largely by additive and dominance effects of chromosomes 2 and 3 and by epistatic interactions involving all four chromosomes. Chaeta number is determined largely by chromosomes with additive effects. For both traits, however, the three- and four-factor epistatic interactions contributed a real and important fraction of the total variance.The data are consistent with the view that egg production has been subjected to directional selection and that chaeta number has been subjected to stabilizing selection.