Consider three different recessive mutations in Drosophila : sc causes scute (fl

Question

Consider three different recessive mutations in Drosophila: sc causes scute (flattened) bristles, s causes sable body color, and v causes vermilion eye color. The wild type phenotypes for each gene are normal bristles, gray body color, and red eye color, respectively. A female heterozygous for these three linked genes is crossed with a male showing recessive phenotype for all three traits. The resulting offspring are shown below. A plus sign indicates wild type phenotype:

scute + + 22

Which offspring classes are recombinant, which represent single crossovers, and which represent double crossovers?

What is the order of the genes on the chromosome?

What are the distances between adjacent genes?

Draw a linkage map of these genes, showing them in their correct order. Indicate on the map the distances between the genes.

Phenotype Phenotype phenotype Number of progeny Scute sable vermilion 1 + + + 3 Scute sable + 3 + + vermillion 399 scute + vermilion 76 + sable + 80 + sable vermilion 23

Explanation / Answer

+ + vermilion 399

+ sable + 80

scute + vermilion 76

+ sable vermilion 23

scute + + 22

+ + + 3

scute sable + 3

scute sable vermilion 1

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