Breeding of Vegetable, Spice and Tuber crops (2+1)

Genetic advance under selection

• Selection of necessity is made on the basis of phenotype, and phenotype is produced by the joint action of genotype and environment. Therefore, the phenotypic superiority of selected plants or families over the original population is not solely due to their genotypic superiority.
• Improvement in the mean genotypic value of the selected families over that of the base population is known as genetic advance under selection (Gs).
  

Genetic advance under selection depends upon

1. The phenotypic variability among different plants or families in the base population,
   
2. The heritability of the character under selection, and
3. The intensity of selection, i.e., the proportion of plants or families selected. Genetic advance under selection may be calculated as follows.

Gs= (k) (σp) (H)

• Where, Gs is genetic advance under selection, k is selection differential, σp is the phenotypic standard deviation of the base population (the population, which is being subjected to selection), and H is the heritability of the character under selection.
  
• The formula for genetic advance under selection, therefore, may be rewritten as

Gs = (k) (√ Vp) (Vg/Vp)

• The selection differential, k, is based on the mean phenotypic values of the selected lines and of the base population, the phenotypic standard deviation (σp), and the intensity of selection, that is, the proportion of population selected.
  
• The k is expressed in terms of standard deviation units. Therefore, the value of k varies with the intensity of selection.