Origin of variation in pure lines
Pure lines show genetic variation after some time because of the following reasons.
- Mechanical Mixture: During cultivation, harvesting threshing and storage, other genotypes may get mixed up.
- Natural hybridization: Through pure lines are produced in self-pollinated crops, some amount of natural cross pollination occurs in them also can be avoided by isolation and rouging.
- Mutation: occur spontaneously in nature at random
Genetic Advance
- Genetic advance is the difference between the mean of the selected plants in the original population and the mean of the progeny raised from the selected plants in the next generation. It can be predicted by the following formula.
Genetic advance (GA) = s P * H * K
K = selection intensity 2.06 when 5% of the population is selected
P = phenotypic standard deviation of the character in the population
H = heritability in broadsense
Genetic gain
- Genetic gain from selection, or simply “genetic gain,” is defined as the improvement in average genetic value in a population or the improvement in average phenotypic value due to selection within a population over cycles of breeding (Hazel and Lush, 1942).
- It is calculated by following formula:
Genetic gain=selection differential *heritability/generation interval.