Question

In Drosophila melanogaster, the allele n gives notched wings while the wildtype allele n⁺ gives normal wings. At a separate gene, the allele sb gives stubby legs while wildtype sb⁺ allele gives normal legs. At a third gene, the allele w gives white eyes while wildtype w⁺ allele gives red eyes. A female individual heterozygous for these three genes is testcrossed and 2090 progeny are produced. They are classified as follows: 17 wildtype

15 notched, stubby, white

126 stubby, white

122 notched

817 white

813 notched, stubby

87 stubby

93 notched, white

(Unless otherwise stated, assume a trait not mentioned explicitly in the classification is the wildtype phenotype e.g. 122 notched = 122 notched wings, normal legs, red eyes.)

1. Write out the genotype of the triply heterozygous mother (i.e. draw the alleles in their proper order on the two chromosomes of the triple heterozygote). Explain your reasoning with respect to the frequencies of the different classes of progeny produced.

(4 marks)

2. Draw a genetic map of the three genes on the chromosome indicating map distances (in m.u.) between genes. Show your calculations.

(3 marks)

3. Calculate the interference. Show your calculations.