MEIOTIC MUTATIONS FROM NATURAL-POPULATIONS OF DROSOPHILA-MELANOGASTER

Two meiotic genes from natural populations are described. A female mei otic mutation, mei(1)g13, mapped to 17.4 on the X chromosome, causes n ondisjunction of all homologs except for the fourth chromosomes. In ad dition, it reduces recombination by 10% in the homozygotes and causes 18% increased recombination in the heterozygotes. A male meiotic mutat ion, mei-1223m144, is located on the third chromosome. Although this m utation causes nondisjunction of all chromosomes, each chromosome pair exhibits a different nondisjunction frequency. Large variations in th e sizes of the premature sperm heads observed in the homozygotes may r eflect irregular meiotic pairing and the subsequent abnormal segregati on, resulting in aneuploid chromosome complements.