Question

What map unit (Centimorgan) is adopted in the construction of genetic maps?
A. A unit of distance between two expressed genes representing cross over.
B. A unit of distance between two expressed genes representing cross over.
C. A unit of distance between genes on chromosomes, representing cross over.
D. A unit of distance between genes on chromosomes, representing cross over.

Answer 1

Genetic mapping is used for the identification of the gene locus as well as the distance between the genes. Genes are used in the construction of genome maps which are used to understand the position and behavior of the genes. They are based on genetic linkage information.

Complete answer:
A centimorgan is a unit which is used for measuring genetic linkage. One centimorgan represents a one percent possibility that a chromosomal marker will be separated from a second marker on the same chromosome and this is taking place due to crossing over in a single generation. Generally, it transforms into approximately one million base pairs of DNA sequences in the human genome.
The unit centimorgan is named after the American scientist Thomas Hunt Morgan. He did his research on fruit flies. He explained the capacity of one part of a genome to separate from another in going from one generation to another.
As there in every generation chromosome transfers pieces of information which are also called recombination, that’s why it is important. This is also important to initiate genetic diversity into the population. And the unit centimorgan defines the rate at which this happens.
Here the terms ‘Centi’ denotes one-hundredth of, and a ‘morgan’ refers to the total recombination of all markers in one part of a chromosome which will become separated from all others. Hence, a centimorgan is the length of DNA over which that takes place only one out of a hundred times or one percent of the time i.e. one percent recombination equals a centimorgan. So, one map unit represents 1% crossover. This centimorgan depends on individual genomes what the distance that a centimorgan represents. It is often used to guess the distance along a chromosome but this map unit is not a true physical distance.

Hence, the correct answer is option (C).

Note: A centimorgan or map unit is a unit which is used for the measurement of genetic distance. This genetic distance is calculated based on the average number of crossover frequencies. Generally, one map unit denotes one percent crossover. This is important for the recombination of chromosomes and genetic diversity into the population.