In a cross of two pure-breeding lines of tomatoes producing different fruit sizes, the variance in grams (g) of fruit weight in the F₁ is 2.25 g and the variance among the F₂ is 5.40 g. Determine the genetic and environmental variance (VG and VE) for the trait and the broad sense heritability of the trait.

Key Concepts

Genetic Variance (VG)

Genetic variance (VG) refers to the portion of phenotypic variance in a trait that can be attributed to genetic differences among individuals. In the context of the tomato cross, VG can be calculated by considering the differences in fruit weight between the F₁ and F₂ generations, as these generations reflect the genetic contributions from the parent lines.

Environmental Variance (VE)

Environmental variance (VE) is the component of phenotypic variance that arises from environmental factors affecting individuals, rather than genetic differences. In this tomato example, VE can be determined by subtracting VG from the total phenotypic variance observed in the F₂ generation, highlighting how much of the variance in fruit weight is due to external conditions.

Broad-Sense Heritability (H²)

Broad-sense heritability (H²) is a measure of the proportion of total phenotypic variance that is attributable to genetic variance. It is calculated as the ratio of VG to the total phenotypic variance (VP). In this case, understanding H² helps assess the extent to which genetic factors influence fruit weight in tomatoes, guiding breeding decisions.