Gce Model Questions Vol1 2020 Biology Question 10

In a certain species of fruit fly, two genes A and B are located on the same chromosome and are linked. The dominant alleles are A and B, the recessive alleles are a and b. The known recombination frequency between the loci is 12 %. A heterozygous individual of genotype AB/ab (cis configuration) is crossed with a homozygous recessive individual aa bb. Answer the following: a) List all possible gamete types produced by the heterozygote and give their expected frequencies. b) Using the gamete frequencies from (a), determine the phenotypic ratio expected among the progeny of the test cross. c) In an actual test cross, 200 offspring are obtained. 112 display the parental phenotypes (both dominant or both recessive) and 88 display recombinant phenotypes. Calculate the experimental recombination frequency and comment on what this indicates about the linkage of A and B. d) Briefly explain how crossing‑over during meiosis generates the recombinant gametes and why the experimentally observed recombination frequency may differ from the map distance of 12 %.