Homozygous XXY lines were established from the tests of primary non-disjunction in three inbred lines of Drosophila melanogaster.The frequency of secondary non-disjunction was shown to differ between the three lines, as well as their brood-pattern. The means of the frequencies of secondary non-disjunction were 1, 2 and 4 %, respectively.The frequency of secondary non-disjunction for heterozygotes obtained from inter-strain crosses showed a lower mean than the parental line with the highest frequency and also less variation between broods. Autosomal genes had a major influence on the frequencies of secondary non-disjunction. Introduction of a marked Y-chromosome (BSYy+) had no influence on the brood-patterns in the inbred lines. Reciprocal heterozygotes which had the marked Y-chromosome showed a maternal influence with a higher frequency of XXY exceptionals in one direction of crosses. The same mothers gave two types of exceptional males, XY and XO.
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