Question

Determination of linkage and % of crossing over between two linked genes is important because

• A. It helps in the fixation of heterosis in the organism.
• B. It helps in maintaining the heterzygosity in a given population.
• C. It explains coupling and repulsion.
• D. None of the above.

Answer 1

The correct option is C It explains coupling and repulsion.

Repulsion: The occurrence on opposite chromosomes in a double heterozygous of the two mutant alleles of interest. Genetic linkage is the tendency of alleles that are located close together on a chromosome to be inherited together during meiosis. Genes whose loci are nearer to each other are less likely to be separated onto different chromatids during chromosomal crossover, and are therefore said to be genetically linked. In other words, the nearer two genes are on a chromosome, the lower is the chance of a swap occurring between them, and the more likely they are to be inherited together.
Coupling: the occurrence of two specified non-allelic genes from the same parent on the same chromosome.
It is usually a simple matter to determine which of the gametes are recombinant. These are the gametes that are found in the lowest frequency. This is the direct result of the reduced recombination that occurs between two genes that are located close to each other on the same chromosome. Also by looking at the gametes that are most abundant you will be able to determine if the original cross was a coupling or repulsion phase cross. For a coupling phase cross, the most prevalent gametes will be those with two dominant alleles or those with two recessive alleles. For repulsion phase crosses, gametes containing one dominant and one recessive allele will be most abundant.