Genetics: L8-A, Calculating genetic distance from offspring phenotypes (Recommend 1.5x Speed)

This video from a university genetics course explains how to calculate genetic distance between two genes based on offspring phenotypes. It begins by introducing the concept of linked genes and the notation for allele arrangement on homologous chromosomes. The instructor describes the four types of gametes produced by a heterozygous individual, distinguishing non-recombinant from recombinant gametes. To determine the frequency of recombinant gametes, a test cross with a homozygous recessive individual is performed, allowing the inference of gamete genotypes from offspring phenotypes. The video then illustrates the origin of recombinant gametes through crossing over during meiosis, showing how chiasmata lead to genetic variation. Using hypothetical offspring counts (e.g., 498, 497, 2, 3), the instructor calculates the recombination frequency as 0.5%, which corresponds to a genetic distance of 0.5 centimorgans. The distinction between genetic and physical distance is explained, noting that genetic distance is based on recombination frequency while physical distance is based on base pairs. The video concludes by emphasizing the correlation between the two measures and the historical significance of genetic distance.