The crossover percentage between two different genes is:

• A. always 50% regardless of their location
• B. unrelated to their position on the chromosome
• C. higher for genes that are closely linked
• D. proportional to the physical distance between them on a chromosome

Answer: (D)

Verified step by step guidance

1. Understand that crossover percentage, also known as recombination frequency, measures how often two genes are separated during meiosis due to crossing over.
2. Recall that genes located close together on the same chromosome tend to be inherited together because the chance of a crossover event occurring between them is low.
3. Recognize that as the physical distance between two genes increases, the probability of a crossover event occurring between them also increases, leading to a higher recombination frequency.
4. Know that a recombination frequency of 50% indicates that genes assort independently, which usually means they are either on different chromosomes or very far apart on the same chromosome.
5. Conclude that the crossover percentage is proportional to the physical distance between genes on a chromosome, making it a useful tool for constructing genetic linkage maps.