Four homozygous recessive mutant lines of Drosophila
melanogaster (labeled 1 through 4) showed abnormal leg
coordination, which made their walking highly erratic.
These lines were intercrossed; the
flies are shown in the following grid, in which “+” represents wild-type walking and “−” represents abnormal
walking:
1 2 3 4
1 - + + +
2 + - - +
3 + - - +
4 + + + -
a. What type of test does this analysis represent?
b. How many different genes were mutated in creating
these four lines?
c. Invent wild-type and mutant symbols, and write out
full genotypes for all four lines and for the F1 flies.
d. Do these data tell us which genes are linked? If not,
how could linkage be tested?
e. Do these data tell us the total number of genes taking
part in leg coordination in this animal?
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