Final answer:
Crossing over is more likely to occur between distantly linked genes than between ones close together on a chromosome because closely linked genes tend to be inherited together, reducing the chance for recombination. Gene distance influences the frequency of crossing over, and geneticists utilize this relationship to construct linkage maps.
Step-by-step explanation:
Crossing over is a process that occurs during meiosis, where two homologous chromosomes exchange genetic material. The likelihood of crossing over occurring between two genes depends on their distance from each other on the chromosome. Genes that are close together are less likely to undergo crossing over because they are more tightly linked, meaning their alleles are often inherited together. This tight linkage limits the occurrence of crossing over between them. In contrast, genes that are farther apart have a higher chance of being separated by crossing over, resulting in a higher frequency of recombination.
Geneticists use the frequency of recombination to map genes on chromosomes. As the distance between two genes increases, so too does the probability of one or more crossover events occurring between them, which can create gametes with nonparental (recombinant) genotypes. These recombinant gametes are important for creating genetic diversity. The linkage maps created by geneticists help illustrate how the genetic distance between genes influences their likelihood to cross over.
Because of crossing over, distant genes on the same chromosome can behave as if they are not linked, further underscoring the role of gene distance in recombination. Therefore, the correct answer to the student's question is that crossing over occurs more frequently between two distantly linked genes than between two genes that are very close together because close genes are more tightly linked, limiting the occurrence of crossing over.