Practice question

Tetratype tetrads predominantly arise from single crossover between two markers involving two chromatids out of four, generating half recombinant chromatids and half parental chromatids within same ascus. Double crossover combinations involving three or four chromatids also can produce TT but less frequent due to positive interference reducing nearby second exchange probability. Therefore TT frequency broadly mirrors single crossover probability and increases roughly proportionally with map distance for close to moderate intervals under 30 cM, providing numerator for recombination estimation via TT divided two proportion. NPD arising solely from double exchanges contributes minor secondary correction.