Biochemistry Term: Linkage Disequilibrium
Linkage disequilibrium (LD) is a concept in genetics and biochemistry that describes the non-random association or correlation between alleles at different loci (locations) within a given DNA sequence.
In other words, when certain genetic variants or alleles at two or more loci tend to be inherited together more frequently than would be expected by chance, they are said to be in linkage disequilibrium. LD is a fundamental aspect of the genetic architecture of populations and has important implications for understanding the inheritance patterns of genetic variations.
LD arises due to the physical proximity of genes on the same chromosome. Genes that are physically close to each other are more likely to be inherited together during the process of genetic recombination, which occurs during the formation of gametes (sperm and egg cells).
While recombination typically shuffles genetic material, breaking up associations between alleles, LD can persist when recombination events are relatively infrequent or when there are specific factors that maintain the association between alleles over time.
The study of LD is crucial for various applications in genetics, including mapping disease-associated genes, understanding population history, and facilitating the design and interpretation of genetic association studies. In genetic association studies, researchers often look for associations between specific genetic markers and traits or diseases.
LD can influence these associations because if two markers are in strong LD, a variation in one marker might be associated with a trait even if the actual causative variant is at the other marker.
In population genetics, LD provides insights into the demographic history of populations. The patterns of LD across the genome can reflect historical events such as population expansions, contractions, migrations, and admixture. By analyzing LD patterns, researchers can gain a better understanding of the genetic diversity and evolutionary dynamics of different human populations.
Advancements in genomics technologies and large-scale genetic studies have facilitated the comprehensive characterization of LD patterns across the human genome. The HapMap and 1000 Genomes Project, for example, have provided extensive LD maps, allowing researchers to identify haplotype blocks—regions of the genome where LD is strong and where genetic variation tends to be inherited together.
Understanding LD is essential for interpreting genetic data accurately and making meaningful inferences about the genetic basis of traits and diseases. It also plays a crucial role in the design of genetic studies and the development of strategies for fine-mapping and identifying causal genetic variants.
