Dosage dependence of maternal contribution to somatic cell division in Drosophila melanogaster.

Most mitotic mutants in Drosophila do not lead to lethality in early development despite the highly abnormal chromosome behaviour that they elicit. This has been explained as being the effect of maternally provided wild-type products. We have tested this hypothesis by studying cuticular clones derived from cells in which there has been loss of a marked Y chromosome due to chromosome nondisjunction in individuals homozygous for the mutation abnormal spindle who are progeny of heterozygous mothers. We have found that the size and frequency of these clones are higher than in control flies. Furthermore, by analysing flies whose female parents have different doses of the asp+ gene, we have found that there is a correlation between the amount of maternally contributed asp+ product and the frequency and size of cuticular clones. We have also estimated the time in development when the first mitotic mistakes take place, i.e. the time when maternal products are no longer sufficient to carry out normal cell division.