A What map unit (Centimorgan) is adopted in the construction of genetic maps?
- A unit of distance between two expressed genes, representing 100% cross over.
- A unit of distance between two expressed genes, representing 100% cross over.
- A unit of distance between genes on chromosomes, representing 1% cross over.
- A unit of distance between genes on chromosomes, representing 50% cross over.
The Correct Option is C
Solution and Explanation
To understand the concept of a map unit, also known as a centimorgan (cM), used in the construction of genetic maps, let's consider the provided options. The goal is to determine which option accurately represents what a centimorgan is.
A genetic map demonstrates the arrangement of genes and the distances between them on a chromosome. These distances are typically measured in centimorgans (cM), named after the geneticist Thomas Hunt Morgan.
- Option 1: "A unit of distance between two expressed genes, representing 100% cross over."
- Option 2: "A unit of distance between two expressed genes, representing 100% cross over." (Identical to Option 1 and therefore, not a viable choice).
- Option 3: "A unit of distance between genes on chromosomes, representing 1% cross over."
- Option 4: "A unit of distance between genes on chromosomes, representing 50% cross over."
Explanation:
A centimorgan corresponds to a 1% probability of recombination, or crossover, occurring between two genes during meiosis. Therefore, the correct definition of a centimorgan is a unit of genetic distance that correlates to 1% recombination frequency between genes on a chromosome. This is not about total crossover, but rather about the likelihood of a single crossover event between two loci on a chromosome.
Based on this understanding, Option 3: "A unit of distance between genes on chromosomes, representing 1% cross over," is the correct answer. This option correctly defines a centimorgan as representing a 1% crossover rate between genes on a chromosome, which is the standard definition in genetic mapping.
Conclusion:
The correct option is: A unit of distance between genes on chromosomes, representing 1% cross over. This aligns with the standard genetic mapping practice and understanding of centimorgan distances.
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