The effect of multi-locus deletions in heterozygotes; a model study using Drosophila.

In a model study using Drosophila, we examined the heterozygous effects of a number of well-defined X-chromosomal deletions (i.e., those differing in location, but of about the same length, and those differing in length but located in the same general region), using relative viability and/or fertility as indicators. Most of the deletions were originally isolated in radiation or chemical mutagenesis experiments and maintained since then in stocks using appropriate balancer chromosomes. The results show that (i) most of the deletions have pronounced deleterious effects in heterozygotes; (ii) the size of the deletion per se is not a critical factor in determining relative heterozygous viability, but its location is and (iii) it is possible to tentatively identify, with respect to the deletions, putative genes that affect viability in Drosophila.