Final answer:
The correct completion for the sentence is "farther," indicating that genes located further apart on a chromosome are more likely to experience a double crossover event. This increases the probability of recombination and results in genetic maps based on recombination frequencies.
Step-by-step explanation:
The blank in the question should be filled with "farther" to correctly complete the sentence: The farther apart the genes, the more likely a double crossover event will occur. This is because genes that are more distant from each other on a chromosome have a higher probability of being separated by a crossover event during meiosis, resulting in genetic recombination.
If the recombination frequency between two genes is less than 50 percent, they are considered to be linked, meaning they are located on the same chromosome and inherited together more frequently than not. However, as the distance between two linked genes increases, so does the likelihood of recombination, meaning that offspring will exhibit a greater proportion of nonparental genotypes. Geneticists utilize recombination frequency data to construct genetic maps, measuring genetic distance in map units or centimorgans (cM), where 1 cM corresponds to a 1% recombination frequency. This mapping of genes on chromosomes is crucial for understanding inheritance patterns and predicting genetic outcomes.