Final answer:
Broad sense heritability estimates are not very practical for breeding programs because they include non-additive genetic variances that are not reliably passed on to offspring and do not account for gene transfer between unrelated species. Breeding focuses on additive genetic variance for selection of traits, making narrow sense heritability a more useful measure for breeders.
Step-by-step explanation:
Broad sense heritability estimates are not very useful in animal and plant breeding programs because they include both additive and non-additive genetic variances. Additive variance refers to the sum of the average effects of individual alleles that can be passed from parents to their offspring. Non-additive variances, such as dominance and epistasis, do not consistently pass from parents to offspring. In breeding programs, the focus is typically on the selection for additive genetic variance as this is what can be reliably transmitted to the next generation, influencing traits in a predictable way. Additionally, broad sense heritability does not account for gene transfer between unrelated species, a factor that can be especially important considering horizontal gene transfer. This is a limitation in comparison to modern genetic engineering techniques which can be more targeted. The importance of genetic diversity and the avoidance of inbreeding depression is critical, as it affects not only the fitness of individual organisms but also the robustness of crop yields and the viability of livestock. By focusing on narrow sense heritability, which only includes additive genetic variations, breeders and farmers can more effectively select for desirable traits and ensure the long-term success of their breeding programs. In contrast, broad sense heritability, while informative about the proportion of phenotypic variation due to all genetic variances, is less practical for the purposes of selective breeding.