Identity by type
s have identity by type 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 because they arose from the same allele in an earlier generation; and those that are non-identical by descent because they arose from separate mutations. NIBD can also be identical by state though, if they share the same mutational expression but not through a recent common ancestor. Parent-offspring pairs share 50% of their genes IBD, and monozygotic twins share 100% IBD.
