Final answer:
Narrow-sense heritability (h2) quantifies the genetic contribution to trait variation within a population, and high heritability means a trait is more likely to be passed on, thereby influencing the effectiveness of selection. Selection can lead to evolutionary changes if the trait has sufficient heritable variation. However, factors like inbreeding can reduce genetic diversity, limiting the impact of selection.
Step-by-step explanation:
The relationship between narrow-sense heritability index (h2) and the impact of selection is that heritability measures how much of the variation in a trait can be attributed to genetic differences. The higher the heritability of a trait, the greater the expected response to selection. When a population undergoes selection, the traits with higher heritability are more likely to be passed on to the next generation, which can lead to a more rapid change in the population's genetic makeup.
Selection acts on the genetic variation available within a population. If a trait that is advantageous for survival and reproduction has high heritability, selection for that trait can lead to an increase in its frequency over time, thereby affecting the population's fitness. However, the efficacy of selection is limited by the amount of genetic variation present, as natural selection cannot create new alleles but can only sort through existing ones.
In understanding how the heritability of traits influences selection, it's important to consider factors such as inbreeding, which can reduce genetic diversity and thus affect the potential for selection to drive evolutionary change. Furthermore, another key factor is the existing genetic variation, which is the raw material upon which selection acts, and without sufficient variation, the ability of a population to adapt and evolve can be significantly reduced.