Which of the following factors does NOT influence narrow sense heritability?

Narrow sense heritability specifically measures the proportion of phenotypic variance in a trait that can be attributed to additive genetic variance. This concept is crucial for understanding how traits are passed from parents to offspring and how they might respond to natural selection.

The correct choice indicates that the specific interactions between different gene loci, often referred to as epistatic interactions, do not influence narrow sense heritability. Instead, narrow sense heritability focuses on the additive effects of individual alleles rather than the complex interactions between genes. This means that narrow sense heritability does not account for the non-additive interactions that can occur when genes interact, which can influence other forms of heritability but are outside the scope of narrow sense heritability.

In contrast, the other factors listed, such as genetic similarities among individuals, environmental conditions affecting the population, and the average genetic contribution of parents to progeny, directly contribute to the evaluation of narrow sense heritability by affecting how traits are expressed and passed on in populations. Thus, understanding these dynamics is key to estimating heritability effectively.