Allele
An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution.
::"The chro ...
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, 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 a sufficiently larg ...
, when they have the same
DNA sequence
DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, guanine, cytosine, and thymine. Th ...
.
Alleles that are identical by type fall into two groups; those that are
identical by descent
A DNA segment is identical by state (IBS) in two or more individuals if they have identical nucleotide sequences in this segment. An IBS segment is identical by descent (IBD) in two or more individuals if they have inherited it from a common an ...
(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, mi ...
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.
See also
*
Population genetics
Population genetics is a subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and pop ...
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
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