Practice question

Two-point cross analyzes segregation of only two markers in testcross progeny, crossing heterozygote to homozygous recessive tester. Scoring parental versus recombinant phenotypes provides recombination fraction RF = recombinant/total ×100, estimating map distance in centimorgans between that specific pair. Method cannot resolve order when more than two genes involved because middle gene remains ambiguous, and cannot detect double crossovers that restore parental configuration leading to underestimation for longer intervals. Nevertheless two-point provides foundational distance estimate essential before undertaking more informative three-point crosses.