Linkage disequilibrium

Definition

Linkage disequilibrium is a non-random association of alleles at different loci in a given population. This phenomenon occurs when the frequency of certain allele combinations is higher or lower than what would be expected under independent assortment, often due to non-random mating patterns, such as assortative mating. It is an important concept in understanding how genetic variation is structured within populations and how it can affect evolutionary processes.

5 Must Know Facts For Your Next Test

1. Linkage disequilibrium can arise from physical proximity of genes on the same chromosome, leading to them being inherited together more often than by chance.
2. It is often measured using the coefficient D or r², which quantify the strength of the association between alleles at different loci.
3. Linkage disequilibrium can be influenced by factors such as selection, genetic drift, mutation, and non-random mating practices.
4. High levels of linkage disequilibrium in a population can indicate recent selective pressure or a historical bottleneck event.
5. Understanding linkage disequilibrium is crucial for mapping quantitative trait loci (QTL) and for association studies in genomics.

Review Questions

• How does non-random mating contribute to linkage disequilibrium in populations?
  • Non-random mating, particularly assortative mating, can significantly contribute to linkage disequilibrium by increasing the likelihood that specific allele combinations are passed on together. When individuals preferentially mate with others who have similar genotypes or phenotypes, certain allele pairs become associated more frequently than expected. This creates a non-random distribution of alleles at different loci, which can skew genetic variation in the population.
• Discuss the relationship between linkage disequilibrium and genetic drift, and how both influence evolutionary processes.
  • Linkage disequilibrium and genetic drift are intertwined in their effects on evolutionary dynamics. Genetic drift can lead to random fluctuations in allele frequencies within small populations, potentially creating or breaking down linkage disequilibrium over time. As alleles become fixed or lost due to drift, their associations may also change. This interaction affects how populations respond to selection pressures and can influence patterns of evolution by altering the genetic structure within populations.
• Evaluate the implications of linkage disequilibrium for genome-wide association studies (GWAS) and how it affects our understanding of complex traits.
  • Linkage disequilibrium plays a critical role in genome-wide association studies (GWAS), as it helps researchers identify regions of the genome associated with complex traits. High levels of linkage disequilibrium enable scientists to use genetic markers that may not be directly involved in trait expression but are correlated with causal variants due to their proximity. This understanding allows for more effective mapping of genetic influences on complex traits and diseases. However, reliance on linkage disequilibrium also presents challenges, as it can lead to false associations if the underlying causal relationships are not accurately identified.

Related terms

Haplotype: A combination of alleles at multiple loci that are inherited together from a single parent.

Genetic Drift: A mechanism of evolution that involves random changes in allele frequencies within a population, which can affect linkage disequilibrium.

Assortative Mating: A form of non-random mating where individuals with similar phenotypes or genotypes are more likely to mate with one another.