Question

In chromosome mapping, one map unit represents
A. the distance between one gene and the next on a chromosome.
B. 1% crossing over between two sites on a chromosome.
C. 1% of the length of the chromosome
D. 10% crossing over between two sites on chromosomes.

Answer 1

Hint: Genetic linkage is the tendency of DNA sequences to be inherited together when they are close together on a chromosome.

Complete answer:
When genes are present on the same chromosomes, they have a tendency to be linked. They have a tendency to stay together during the process of meiosis. When the chromosomes segregate, there occurs some crossing over of DNA. As a result of which, the alleles on the same chromosomes separate and are received by different daughter cells. The alleles that are far apart on the chromosome are more likely to undergo crossing over.
The differences in the recombinant frequencies is found to be associated with the distance between the genes and the recombinant frequencies are used to determine the positions which are referred to as loci. The loci or position of the genes in the chromosomes are important and used in preparing chromosome maps.
A chromosome map is thus a graphical representation of formation of linkage groups in the form of a line which determines the relative distances between the genes it contains. A chromosome map is also called a genetic map or linkage map. The process of preparing chromosome maps of a species is known as chromosome mapping.
The technique utilizes the method of working out the number of recombinants and obtaining a measure for the distance between them.
The distance between the genes in which one product of meiosis in 100 is recombinant is known as a genetic map unit or map unit. One map unit is equal to 1% of recombinant frequency. Hence, map unit is equal to the crossing over between the chromosomes. A map unit is also known as centimorgan.

>Hence, the option (B) is the correct and best suited option.

Note: A linkage map is created by calculating the distance between the alleles on the same chromosomes and estimating as well as avoiding gaps between the alleles to avoid possibilities of many crossovers