In a line of cherry tomatoes, the average fruit weight is 16 g. A plant producing tomatoes with an average weight of 12 g is used in one self-fertilization cross to produce a line of smaller tomatoes, and a plant producing tomatoes of 24 g is used in a second cross to produce larger tomatoes. What is the selection differential (S) for fruit weight in each cross?

Key Concepts

Selection Differential (S)

The selection differential (S) is a measure of the difference between the mean phenotype of the selected individuals and the mean phenotype of the entire population. It quantifies the extent to which selected individuals differ from the average, indicating the strength of selection. In this context, S can be calculated by subtracting the average fruit weight of the selected plants (12 g or 24 g) from the average fruit weight of the original population (16 g).

Phenotypic Variation

Phenotypic variation refers to the observable differences in traits among individuals in a population, which can be influenced by genetic and environmental factors. Understanding phenotypic variation is crucial for predicting how traits like fruit weight can change over generations due to selection. In this scenario, the variation in fruit weight among the selected plants and the original population is essential for calculating the selection differential.

Self-Fertilization in Plants

Self-fertilization is a reproductive strategy where a plant fertilizes its own ovules, leading to offspring that are genetically similar to the parent. This method can stabilize certain traits within a population, making it easier to observe the effects of selection on specific characteristics, such as fruit weight. In the given question, self-fertilization is used to produce lines of tomatoes with distinct average weights, which are critical for calculating the selection differentials.