Identity by descent (IBD) and identity by state (IBS) are terms used in genetics to describe the relationship between alleles at a particular locus in different individuals.
IBD is when two or more individuals share an identical DNA sequence at a given locus because they inherited that DNA sequence from a common ancestor. In other words, they have the same alleles at that locus because they were passed down to them from the same ancestor. IBD can be detected through techniques such as linkage analysis and haplotype analysis.
On the other hand, IBS refers to the situation where two or more individuals share identical alleles at a given locus, but not necessarily because they inherited those alleles from a common ancestor. Instead, they may have independently acquired them due to chance. IBS can be detected through techniques such as allele frequency analysis.
Here’s a quick comparison chart between IBD and IBS.
| Identity by Descent (IBD) | Identity by State (IBS) | |
|---|---|---|
| Definition | Occurs when two or more individuals share identical alleles at a given locus because they inherited them from a common ancestor | Occurs when two or more individuals share identical alleles at a given locus, but not necessarily because they inherited them from a common ancestor |
| Detection Methods | Linkage analysis, haplotype analysis | Allele frequency analysis |
| Relationship between individuals | Indicates a genetic relationship between individuals due to inheritance from a common ancestor | Indicates a genetic relationship between individuals based solely on their shared alleles, regardless of whether or not they inherited them from a common ancestor |
| Significance | Helpful in identifying shared genetic ancestry and tracing genealogical relationships | Helpful in analyzing population genetics and detecting genetic variations |
| Occurrence | Rare | Common |
| Examples | Identical twins, parent-child, siblings | Unrelated individuals who happen to have identical alleles at a particular locus |
To summarize, IBD describes a genetic relationship between individuals due to inheritance from a common ancestor. In contrast, IBS describes a genetic connection between individuals based solely on their shared alleles, regardless of whether or not they inherited them from a common ancestor.
