Quantitative Trait Analysis and Heritability

Quantitative Trait Analysis

• Quantitative traits are traits that show continuous variation, like height, weight, or blood pressure
• Quantitative traits are influenced by multiple genes and environmental factors
• Quantitative traits can be measured and analyzed statistically to study genetic and environmental contributions

Heritability

• Heritability measures the proportion of phenotypic variation in a population that is attributable to genetic variation
• Heritability does not tell us about specific genes involved

Broad Sense Heritability (H2)

• H2 is the proportion of phenotypic variation attributable to all genetic variation, including additive, dominance, and epistatic effects
• H2 is calculated as the ratio of genetic variance (VG) to total phenotypic variance (VP)
• H2 ranges from 0 to 1

Understanding H2

• High H2 (close to 1) implies that genotype is a major factor in determining the trait
• It does not mean that the trait is entirely determined by genes or that an individual's phenotype can be predicted based on their parents' phenotypes
• H2 is specific to a particular family or population, and does not generalize to other populations

Limitations of H2

• H2 does not tell us how much of the variation is due to additive genetic effects, which are the effects that can be passed on to offspring
• H2 is calculated based on the total variance in a population, and does not account for the specific genetic variants that contribute to a trait

Narrow Sense Heritability (h2)

• h2 is the proportion of phenotypic variation due to additive genetic variation
• h2 is calculated as the ratio of additive genetic variance (VA) to total phenotypic variance (VP)
• h2 is important for predicting the response to selection in breeding programs

Understanding h2

• High h2 implies that the trait is more strongly influenced by additive genetic effects, allowing for greater prediction of offspring phenotype based on parental phenotype
• h2 is still specific to a particular family or population
• h2 does not tell us which genes are involved

Applications of Heritability

• Heritability estimates can be used to identify individuals with specific traits for breeding purposes
• Heritability estimates can be used to predict the impact of genetic interventions on a population
• Heritability estimates can help researchers understand the genetic basis of complex traits