identicalbydescent

identicalbydescent refers to two or more individuals who share a common ancestor. This concept is fundamental in genetics and genealogy. When individuals are identical by descent, it means they have inherited the same segments of DNA from a shared relative. This is distinct from being identical in the sense of identical twins, who are a specific case of being identical by descent from their parents.

The degree of genetic sharing between individuals identical by descent depends on their relationship. For example, siblings share, on average, 50% of their DNA, while first cousins share, on average, 12.5%. The more recent the common ancestor, the greater the proportion of DNA that is likely to be identical by descent.

In genealogical research, identifying individuals identical by descent can help confirm relationships and reconstruct family trees. Genetic genealogy services often use algorithms to estimate the length and number of DNA segments shared between individuals, which can then be used to infer their most recent common ancestor and thus their degree of relatedness. This method is a powerful tool for understanding ancestry and kinship.

The concept is also relevant in medical genetics, as inheriting identical DNA segments from a common ancestor can sometimes increase the risk of carrying certain genetic conditions if that ancestor was a carrier. Understanding identical by descent helps in tracing the inheritance patterns of genes within families.