The genetic analysis of distributive segregation in Drosophila melanogaster. I. Isolation and characterization of Aberrant X segregation (Axs), a mutation defective in chromosome partner choice.
We describe the isolation and characterization of Aberrant X segregation (Axs), a dominant female-specific meiotic mutation. Although Axs has little or no effect on the frequency or distribution of exchange, or on the disjunction of exchange bivalents, nonexchange X chromosomes undergo nondisjunction at high frequencies in Axs/+ and Axs/Axs females. This increased X chromosome nondisjunction is shown to be a consequence of an Axs-induced defect in distributive segregation. In Axs-bearing females, fourth chromosome nondisjunction is observed only in the presence of nonexchange X chromosomes and is argued to be the result of improper X and fourth chromosome associations within the distributive system. In XX females bearing a compound fourth chromosome, the frequency of nonhomologous disjunction of the X chromosomes from the compound fourth chromosome is shown to account for at least 80% of the total X nondisjunction observed. In addition, Axs diminishes or ablates the capacity of nonexchange X chromosomes to form trivalents in females bearing either a Y chromosome or a small free duplication for the X. Axs also impairs compound X from Y segregation. The effect of Axs on these segregations parallels the defects observed for homologous nonexchange X chromosome disjunction in Axs females. In addition to its dramatic effects on the X chromosome, Axs exerts a similar effect on the segregation of a major autosome. We conclude that Axs defines a locus required for proper homolog disjunction within the distributive system.
Zitron
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Department of Molecular Genetics, Albert Einstein College of Medicine, Bronx, New York 10464.
Hawley
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D000818:Animals; D007446:Chromosome Inversion; D002874:Chromosome Mapping; D003433:Crosses, Genetic; D004331:Drosophila melanogaster / Q000235:genetics*; D005260:Female; D005799:Genes, Dominant; D005838:Genotype; D006579:Heterozygote; D008297:Male; D009154:Mutation; D009630:Nondisjunction, Genetic; D010641:Phenotype; D011995:Recombination, Genetic; D014960:X Chromosome