Explain why independent assortment may not occur for genes that are close together on the same chromosome and how recombination frequency is used.

• A. Linked genes tend to be inherited together; recombination frequency (percentage of recombinant offspring) measures distance between them on the chromosome.
• B. Independent assortment occurs regardless of distance.
• C. Recombination frequency indicates mating patterns.
• D. Distance between genes is measured by gene expression.

Answer: (A)

When genes are close together on the same chromosome, they are linked and tend to be inherited as a unit rather than independently. This is because a single crossing over event between them is less likely to occur, so the original allele combination on that chromosome is passed down more often intact. However, crossing over can still happen during meiosis, and when it does occur between the two genes, it creates new allele combinations—the recombinant types. The closer the genes are, the rarer these crossing-over events, so the parental combinations dominate and independent assortment isn’t observed as strongly.

Recombination frequency measures how often those new combinations appear among offspring. It’s calculated as the number of recombinant offspring divided by the total number of offspring, times 100 to give a percentage. This value serves as a proxy for the distance between the genes on the chromosome: a higher recombination frequency means a greater distance, and as the distance increases toward about 50%, the genes behave more like they assort independently. That 50% figure also marks the point where genes on different chromosomes show independent assortment, so recombination frequency is used to create genetic maps in centimorgans, reflecting how far apart the genes are on the chromosome.