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The concept of heritability plays a crucial role in genetics and breeding, serving as a measure of the extent to which genetic variation contributes to the variability observed in a specific trait within a population. It offers valuable insights into the potential for selective breeding to modify or enhance particular traits. There exist two primary types of heritability:
Broad-Sense Heritability (H²): Broad-sense heritability quantifies the proportion of phenotypic variation in a trait that can be ascribed to genetic factors. This encompasses additive genetic effects, dominance effects, and gene interactions. Represented as H², its values range from 0 to 1, with higher values signifying a more significant genetic influence on the trait's expression. In the context of dairy cows, the notable increase in broad-sense heritability for "first lactation milk" from roughly 0.25 in the 1970s to approximately 0.4 today suggests an elevated genetic impact on this trait.
Narrow-Sense Heritability (h²): Narrow-sense heritability specifically gauges the proportion of phenotypic variation attributable to additive genetic effects, which represent the effects of individual genes. It is represented as h² and also varies from 0 to 1. An upsurge in narrow-sense heritability implies an augmented contribution of additive genetic factors to the studied trait.
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