Final answer:
The likelihood that two genes are separated by crossing-over is most directly related to the distance between the genes on the same chromosome. Closer genes have lower chances of being separated by crossing-over and are considered genetically linked, while genes further apart have a higher chance of being recombined. Geneticists use the frequency of recombination to determine the distance between genes, constructing linkage maps of chromosomes.
Step-by-step explanation:
The probability that two genes will be separated by crossing-over is related to the distance between the genes on the same chromosome. During meiosis, the closer two genes are located on the chromosome, the lower the probability they will be separated by crossing-over. This is because genes that are close together are said to be genetically linked and tend to be inherited together as a unit. Conversely, as the distance between two genes increases, the more likely it is for crossing-over to occur, resulting in recombination and the production of gametes with nonparental genotypes.
Geneticists have used the frequency of crossover events, reflected by the proportion of nonparental gametes produced, to construct linkage maps. These maps provide a visual representation of gene order and genetic distances between loci on a chromosome. The recombination frequency informs these distances, expressed in terms of map units or centimorgans (cM), where 1 cM typically corresponds to a 1% recombination frequency. Therefore, a higher recombination frequency indicates that two genes are further apart, while a lower frequency suggests they are closer. To summarize, the probability that two genes will be separated by crossing-over is most directly related to their physical proximity on the same chromosome.