Allele An allele is a variant of the sequence of nucleotides at a particular location, or Locus (genetics), locus, on a DNA molecule. Alleles can differ at a single position through Single-nucleotide polymorphism, single nucleotide polymorphisms (SNP), ...

s 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 In genetics and bioinformatics, a single-nucleotide polymorphism (SNP ; plural SNPs ) is a germline substitution of a single nucleotide at a specific position in the genome. Although certain definitions require the substitution to be present in ...

, when they have the same

DNA sequence A nucleic acid sequence is a succession of bases within the nucleotides forming alleles within a DNA (using GACT) or RNA (GACU) molecule. This succession is denoted by a series of a set of five different letters that indicate the order of the nu ...

. 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

mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, ...

s. NIBD can also be identical by state (IBS) 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.

External links

* https://web.archive.org/web/20060309055031/http://darwin.eeb.uconn.edu/eeb348/lecture-notes/identity.pdf * http://zwets.com/pedkin/thompson.pdf Classical genetics {{genetics-stub

See also

External links