55. One centimorgan is defined as the genetic distance between two loci with a statistically
corrected recombination frequency of:
A. 0.1%
B. 0.5%
C. 1.0%
D. 5.0%

Introduction:

In genetics, centimorgan (cM) is a unit of measurement used to describe the genetic distance between two loci on a chromosome. This measure is essential in constructing genetic maps and understanding the likelihood of recombination events during meiosis. One centimorgan represents a 1% expected recombination frequency between two loci, indicating that there is a 1% chance that a crossover will occur between them during gamete formation.

What is a Centimorgan?

The centimorgan (cM) is named after Thomas Hunt Morgan, a pioneering geneticist. It is a unit used to quantify genetic distance. The closer two loci are on a chromosome, the less likely they are to undergo recombination during meiosis. Recombination occurs when chromosomes exchange genetic material, resulting in new combinations of alleles. The frequency of this recombination is influenced by the physical distance between the loci on the chromosome.

Recombination Frequency and Genetic Mapping:

The recombination frequency is a measure of how often a crossover will occur between two loci during meiosis. It is expressed as a percentage, which is directly correlated to the genetic distance between the loci. The higher the recombination frequency, the greater the genetic distance between the loci.

For example:

• 1% recombination frequency corresponds to 1 centimorgan (cM).

• If two loci have a recombination frequency of 0.5%, the genetic distance between them is 0.5 cM.

• 5% recombination frequency corresponds to 5 cM.

Key Concept: Recombination Frequency

Recombination frequency plays a critical role in determining genetic distances:

• A 0% recombination frequency indicates the loci are genetically linked, meaning they are very close to each other on the chromosome and do not recombine much.

• A 100% recombination frequency means the loci are unlinked, and recombination between them is independent.

However, there is a threshold at which recombination frequencies no longer accurately reflect genetic distances, especially when values exceed 50%. For loci that are far apart on the chromosome, recombination frequencies may saturate at 50%, making it difficult to measure larger distances using recombination alone.

Answering the Question:

The question asks: “One centimorgan is defined as the genetic distance between two loci with a statistically corrected recombination frequency of?”

The correct answer is: C. 1.0%

This means that one centimorgan (cM) corresponds to a 1% recombination frequency. This is the standard definition used in genetic mapping.

Conclusion:

Understanding centimorgan and recombination frequency is fundamental in genetics for constructing accurate genetic maps and studying inheritance patterns. A 1% recombination frequency defines 1 centimorgan, a key concept for geneticists studying linkage and gene mapping.

Answer:

C. 1.0%

For additional information on genetic mapping and recombination, consider exploring the following: