Linkage disequilibrium

Definition

Linkage disequilibrium refers to the non-random association of alleles at different loci in a population, meaning certain combinations of alleles occur together more often than would be expected under random mating. This concept is important for understanding how genetic variants are inherited and can indicate underlying genetic structures, population history, and evolutionary dynamics.

5 Must Know Facts For Your Next Test

1. Linkage disequilibrium can arise due to factors such as selection, genetic drift, population admixture, and the physical proximity of loci on the same chromosome.
2. The degree of linkage disequilibrium is measured by the correlation coefficient 'D', with values ranging from -0.5 to 0.5 indicating varying levels of association between alleles.
3. In populations that have undergone recent admixture, linkage disequilibrium may be more pronounced due to the mixing of previously isolated gene pools.
4. Understanding linkage disequilibrium is essential for mapping complex traits in genome-wide association studies (GWAS) since it can inform researchers about nearby loci that may contribute to a particular phenotype.
5. Linkage disequilibrium generally decreases with increasing physical distance between loci due to recombination events disrupting associations over generations.

Review Questions

• How does linkage disequilibrium differ from linkage equilibrium in terms of allele associations?
  • Linkage disequilibrium differs from linkage equilibrium in that it represents a non-random association of alleles at different loci, meaning some combinations occur together more frequently than expected by chance. In contrast, linkage equilibrium indicates that alleles assort independently, showing no significant correlation between their frequencies. Understanding this difference is key in analyzing genetic variation and inheritance patterns within populations.
• Discuss the factors that can lead to the establishment of linkage disequilibrium in a population.
  • Linkage disequilibrium can be established by several factors including natural selection favoring certain allele combinations, genetic drift in small populations leading to random fluctuations in allele frequencies, and recent population admixture where different gene pools combine. Additionally, physical proximity of loci on chromosomes reduces the likelihood of recombination events breaking down allele associations. These factors collectively shape the genetic landscape and influence evolutionary trajectories within populations.
• Evaluate the implications of linkage disequilibrium for genome-wide association studies (GWAS) and how it can impact trait mapping.
  • Linkage disequilibrium plays a crucial role in genome-wide association studies (GWAS) as it helps researchers identify genetic variants associated with complex traits. When alleles are in linkage disequilibrium, nearby loci are more likely to be inherited together, allowing researchers to pinpoint regions of the genome that may influence traits even if the causal variant is not directly measured. This relationship enhances the power and accuracy of GWAS but also requires careful consideration of population structure and history, as these factors can confound results and lead to false associations.

Related terms

Linkage equilibrium: Linkage equilibrium occurs when alleles at different loci assort independently in a population, resulting in no significant correlation between their frequencies.

Recombination:

Recombination is the process during meiosis where chromosomes exchange segments, leading to new allele combinations and affecting linkage disequilibrium.

Haplotype:

A haplotype is a set of alleles at multiple loci that are inherited together from a single parent, which can show patterns of linkage disequilibrium.