In mosquitos, a dominant allele confers resistance to the insecticide DDT. A dom

Question

In mosquitos, a dominant allele confers resistance to the insecticide DDT. A dominant allele confers resistance to another insecticide called Dieldrin. It is not clear whether these alleles are different variants of the same gene, or if they are different genes, however, they are known to be on the same chromosome. A cross was carried out between two truebreeding strains, a DDT-resistant strain (which was sensitive to Dieldrin) and a Dieldrin-resistant strain (which was sensitive to DDT). Female F1s that were resistant to both insecticides were then testcrossed with wildtype males. The progeny were 99 resistant to both insecticides, 88 resistant to DDT only 89 resistant to Dieldrin only, and 106 sensitive to both insecticides Are DDT and DI alleles of the same gene? O Yes O No can't tell QUESTION 2 How can you tell? Because some offspring from the testcross were resistant to Dieldrin, but not DDT. These offspring can only be produced if recombination occurs between loci Because some offspring from the testcross were resistant to both Dieldrin and DDT. These offspring can only be produced if recombination occurs between loci. Can't tell QUESTION 3 What offspring phenotype ratios do you expect from the testcross if the genes are far apart on the same chromosome? O 50% DDT resistant, 50% dieldrin resistant 100% resistant to both DDT and dieldrin O 100% wild type O 25% DDT resistant, 25% DDT and dieldrin resistant, 25% dieldrin resistant, 25% wild type

Explanation / Answer

1.B

2.A

3. A   The recombination frequency will be 50% when two genes are located on different chromosomes or when they are widely separated on the same chromosome.

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