Principles of Genetics and Breeding

10.1.10 Selection

It is defined as the non-random differential propagation of the genotypes. In other words, selection acts through the differences in fertility of individuals and viability of their progeny. It is a natural process and human being has no-control over it. Selection acts on the phenotype of the next generation and is considered to select in favour by nature. One who contributes the highest number of progeny is called as the fittest individual. Has highest fitness (F=1).

• Nature selection operates through differences in fertility of the parents, which is controlled by genes.
• If the presence or absence of a gene modifies the phenotype in such a way that it leads to change in fertility, we say selection is acting on the gene.
• Thus, the selection that acts directly on the phenotype and therefore on the gene, resulting in change of frequency.
• The degree of selection acting against a gene is called the coefficient of selection (s).
• Coefficient of selection is defined as the proportionate reduction in the gametic contribution of a genotype.

The change in gene frequency due to selection depends on the coefficient of selection or the degree of disadvantage of the phenotype and its frequency in the population.

The above-mentioned results can be utilized in planning long-term selection programmes, especially to reduce the frequency of a deleterious recessive allele. It is of general interest to know the number of generations or years to be required to reduce the frequency of a gene to a particular level.