Final answer:
The genetically heterogeneous variety of tomato plants is likely to have a higher broad sense heritability for fruit size, because genetic diversity introduces more genetic variance, which is a contributing factor to heritability. The exact heritability also depends on how traits manifest, as seen in Mendel's experiments, where dominant and recessive traits played a role in the phenotypic expression.
Step-by-step explanation:
The variety of tomato plants that is more genetically heterogeneous is likely to have a higher broad sense heritability value for fruit size. Heritability in a broad sense is a measure of how much of the variation in a trait is due to genetic factors, encompassing additive, dominance, and epistatic variance. In a more genetically heterogeneous population, there is greater variance to be attributed to genetic factors, leading to a potentially higher heritability. Conversely, a less genetically diverse population could have more of its variation in fruit size due to environmental differences, assuming that the environment has not been completely standardized for both plant varieties, thus lowering heritability.
However, it's important to remember that broader genetic diversity doesn't automatically guarantee a higher heritability for all traits since heritability is specific to each characteristic and the environment in which it is measured. As Gregor Mendel's experiments with peas demonstrated, even with a homozygous genotype, the manifestation of the phenotype can be straightforward, with dominant traits overshadowing recessive ones. Nevertheless, a genetically diverse population can be thought of as a larger 'deck of cards' with more combinations available in the genetic shuffle, thus potentially expressing a wider range of traits and making it a reasonable hypothesis that this increased genetic variance could lead to higher heritability for specific traits like fruit size.