Answer to Question #174323 in Genetics for Malak Sadka

Question

Following a mutagenesis experiment to identify novel genes affecting the circadian clock in Drosophila melanogaster you discover several mutants. Two mutants are named c and d. The two homozygous c/c and d/d are arrhythmic, whereas the two heterozygous C/c and D/d are rhythmic with a 24h period. You make two true-breeding stocks: stock 3 homozygous for c and stock 4 homozygous for d. You cross them in both directions and in both cases you observe complementation with no difference between males and females. Then you take the progeny of one cross, for instance the F1 of Females 3 x Males 4, and you perform a Testcross. Out of 1000 flies resulting from the Testcross only 125 are rhythmic.

Comparing the number of flies expected for the Parental and the Recombinant genotypes, what can be concluded about the C and D loci? (In terms of whether C and D are linked and the ratios of parental to recombinant - more or less?)

Answer 1

The possible F1 genotypes are cc cd cd dd