Final answer:
Missing heritability is the gap between the heritability estimated from pedigree studies and the heritability accounted for by identified genetic markers. This concept highlights the complexity of genetic influences on traits and acknowledges that our genetic knowledge is incomplete.
Step-by-step explanation:
Missing heritability refers to the portion of heritability that cannot be explained by known genetic variants. It is a concept used to describe the gap between the heritability estimated from pedigree analysis or twin studies and the heritability explained by the genetic variants that have been identified so far through genetic association studies, such as SNP analysis (single nucleotide polymorphisms). Although the exact genetic basis of many traits is not fully understood, several factors may contribute to missing heritability, including the influence of rare variants, structural variations, gene-gene interactions (epistasis), gene-environment interactions, and even epigenetic factors. However, these do not all contribute to the definition of missing heritability.
When scientists estimate the heritable variation of a trait within a population, they often find that the identified genetic markers account for only a portion of the expected genetic variance. This discrepancy is what is termed as missing heritability. It suggests that there are more genetic factors at work than those already discovered and that our understanding of the genetic architecture of complex traits is incomplete. This knowledge gap has implications for fields such as genetics, medicine, and evolutionary biology, as it is crucial for the prediction, diagnosis, and treatment of genetic disorders, as well as for understanding the potential for a population's traits to respond to natural selection.