How was it established experimentally that the frequency of recombination (crossing over) between two genes is related to the distance between them along the chromosome?

Genetic recombination occurs during meiosis when homologous chromosomes exchange segments, resulting in new allele combinations. Crossing over is the physical process that facilitates this exchange, and its frequency reflects how often two genes are separated during this event.

Genes located close together on the same chromosome tend to be inherited together, a phenomenon called linkage. By measuring recombination frequencies between gene pairs, scientists can estimate their relative distances, creating genetic maps that represent gene order and spacing.

Recombination frequency is experimentally determined by crossing organisms with known genotypes and analyzing offspring phenotypes. The proportion of recombinant offspring indicates how often crossing over occurs between two genes, allowing researchers to correlate recombination rates with physical gene distances.