Final answer:
When genes are close together on the same chromosome, their alleles tend to be transmitted together during meiosis. As the distance between linked genes increases, the probability of crossovers between them increases. Geneticists use recombination rates to determine the distance between genes on a chromosome.
Step-by-step explanation:
When two genes are located in close proximity on the same chromosome, their alleles tend to be transmitted together during meiosis. This is known as genetic linkage. For example, if one homologous chromosome has alleles for tall plants and red flowers, and the other homologous chromosome has alleles for short plants and yellow flowers, the tall and red alleles will go together into a gamete, and the short and yellow alleles will go into other gametes. This means there will be no gametes with tall and yellow alleles or short and red alleles.
As the distance between two linked genes increases, the probability of crossovers between them increases, and the genes behave more as if they are on separate chromosomes. Geneticists use the proportion of recombinant gametes (the ones not like the parents) as a measure of how far apart genes are on a chromosome. They have constructed linkage maps of genes on chromosomes for well-studied organisms, including humans.