Alleles have identity by type (IBT) when they have the same phenotypic effect, or if applied to a variation in the composition of DNA such as a Single nucleotide polymorphism when they have the same DNA sequence.
Alleles that are identical by type fall into two groups; those that are identical by descent (IBD) because they arose from the same allele in an earlier generation; and those that are non-identical by descent (NIBD) because they arose from separate mutations. NIBD can also be identical by state (IBS) though, if they share the same mutational expression (just not origin). Parent-offspring pairs share 50% of their genes IBD, and monozygotic twins share 100% IBD.
Famous quotes containing the words identity and/or type:
“One of the most highly valued functions of used parents these days is to be the villains of their children’s lives, the people the child blames for any shortcomings or disappointments. But if your identity comes from your parents’ failings, then you remain forever a member of the child generation, stuck and unable to move on to an adulthood in which you identify yourself in terms of what you do, not what has been done to you.”
—Frank Pittman (20th century)
“To be a real philosopher all that is necessary is to hate some one else’s type of thinking.”
—William James (1842–1910)