The alleles his-5 and lys-l, found in bakers yeast, result in cells that require histidine and lysine for growth, respectively. A cross was made between two haploid yeast strains that are his-5 lys-l and his* lys'. From the analysis of 818 individual tetrads, the following numbers of tetrads were obtained:
2 spores: his-5 lys* + 2 spores: his+ lys-l = 4
2 spores: his-5 lys-l + 2 spores: his+ lys+ = 502
1 spore: his-5 lys-l + 1 spore: his-5 lys+ + 1 spore: his+ lys-l + 1 spore: his+ lys* =312
A. Compute the map distance between these two genes using the method of calculation that considers double crossovers and the one that does not. Which method gives a higher value? Explain why.
B. What is the frequency of single crossovers between these two genes?
C. Based on your answer to part B, how many NPDs are expected from this cross? Explain your answer. Is positive interference occurring?