Question

Frequency of crossing-over between linked genes is

• A. Inversely proportional to the distance between them
• B. Proportional to the distance between them
• C. Inversely proportional to the square of the distance between them
• D. Proportional to the square of the distance between them

Hint:

• Linked genes are on the same chromosome.
• Crossing-over during meiosis can separate linked genes.
• The probability (frequency) of a crossover event occurring between two linked genes increases with the physical distance between them on the chromosome.
• Recombination frequency is used to estimate genetic map distances.

Answer 1

The Correct Option is B

Crossing-over (recombination) is the exchange of genetic material between homologous chromosomes during meiosis. Genes that are located on the same chromosome are said to be linked. The frequency of crossing-over between two linked genes is a measure of the genetic distance between them.

• Genes that are farther apart on a chromosome are more likely to have a crossover event occur between them.
• Genes that are very close together are less likely to be separated by a crossover.

Therefore, the frequency of crossing-over (recombination frequency) between linked genes is generally proportional to the physical distance separating them on the chromosome (at least for relatively short distances where multiple crossovers are rare or can be accounted for). This principle is the basis for constructing genetic maps, where 1 map unit (or 1 centimorgan, cM) corresponds to a 1% recombination frequency. So, as distance increases, the frequency of crossing-over increases. \[ \boxed{\text{Proportional to the distance between them}} \]