Table 3.

Distribution of Genotypes Among the Offspring from a Cross Between Male and Female Flies, Being Heterozygous for the P Element Insertion in Exon 1 of the DLGR-2 Gene

	Dead embryos	Third instar larvae	Total
P/P	23	0	23
P/+	2	42	44
+/+	1	20	21

Of 100 eggs collected from a cross, 26 animals died during embryonic development (including both unhatched eggs and larvae that died within 1 hr after hatching), 69 developed into third instar larvae. Five animals disappeared during the experiments. All animals were investigated by PCR to reveal their genotype. For seven of the third instar larvae, the PCR gave no products, so the genotype of these animals is unknown. The dead embryos of the genotype P/+ and +/+ could easily be distinguished from the P/P animals by their less-developed appearance. Dead P/P animals had the gross anatomy of normal, wild-type first-instar larvae. The crossing experiment shows that the mutation is homozygous lethal and that it roughly follows mendelian genetics.