Linkage disequilibrium

Definition

Linkage disequilibrium refers to the non-random association of alleles at two or more loci in a population. This phenomenon occurs when specific combinations of alleles occur together more often than would be expected based on their individual frequencies, suggesting that the loci are physically linked on the same chromosome and are inherited together. Understanding linkage disequilibrium is crucial for studying genetic variation, mapping traits, and understanding evolutionary processes.

5 Must Know Facts For Your Next Test

1. Linkage disequilibrium can arise due to factors such as population bottlenecks, genetic drift, or selection, leading to certain allele combinations being favored.
2. The measure of linkage disequilibrium is often quantified using the coefficient 'D' or 'r²', which assess how much the observed allele combination differs from what would be expected under random assortment.
3. Linkage disequilibrium tends to decrease over generations due to recombination events that shuffle alleles between chromosomes.
4. High levels of linkage disequilibrium are often observed in populations that have undergone recent admixture or where specific selective pressures have been applied.
5. Understanding linkage disequilibrium is essential for genome-wide association studies (GWAS) as it helps identify regions of the genome that may be associated with specific traits or diseases.

Review Questions

• How does linkage disequilibrium influence the inheritance of traits in a population?
  • Linkage disequilibrium influences inheritance by causing certain combinations of alleles at different loci to be passed down together more frequently than expected if they were independently assorted. This non-random association can result in traits being inherited in a way that reflects the physical proximity of the genes on the chromosome. Consequently, if one allele is associated with a particular phenotype, its linked alleles may also contribute to that phenotype, affecting how traits appear in successive generations.
• Discuss the impact of recombination on linkage disequilibrium over time.
  • Recombination plays a critical role in reducing linkage disequilibrium over time by breaking up allele combinations at linked loci. As recombination occurs during meiosis, it creates new allele combinations by mixing alleles between homologous chromosomes. This process leads to a gradual decay of linkage disequilibrium as generations progress, making it less likely for specific allelic combinations to remain associated. Ultimately, higher rates of recombination can lead to lower linkage disequilibrium within populations.
• Evaluate the importance of studying linkage disequilibrium in the context of genome-wide association studies (GWAS).
  • Studying linkage disequilibrium is vital for genome-wide association studies (GWAS) because it helps researchers identify genetic variants associated with complex traits and diseases. By analyzing regions of high linkage disequilibrium, scientists can narrow down candidate genes and polymorphisms that may contribute to phenotypic variation. This understanding enhances the ability to link specific alleles to traits or diseases, paving the way for advancements in personalized medicine and targeted therapies based on an individual's genetic profile.

Related terms

linkage: The tendency of genes located close to each other on a chromosome to be inherited together during meiosis.

recombination: The process by which genetic material is physically mixed during meiosis, leading to the formation of new allele combinations.

haplotype: A combination of alleles at multiple loci that are inherited together as a unit, often used to study genetic associations in populations.