Linkage Disequilibrium

Question 1

What is linkage disequilibrium (and equilibrium) and why does it matter if it’s not an evolutionary force in its own right?

Answer 1

• LD- the state of non-random associations between alleles at multiple loci
• LE- no association among different loci, probabilites of events at both loci are independent
• LD is important because it changes the effect of evolutionary forces

Question 2

What are some of the ways that LD forms?

Answer 2

New mutations forming new physical associations on chromosomes
Can also be driven by founder effect and bottleneck if there is a preexisting mutation

Question 3

What causes populations in LD to return to linkage equilibrium?

Answer 3

Linkage is eroded by recombination

Question 4

What is genetic hitchhiking? Why does it matter?

Answer 4

• Genetic hitchhiking- positive natural selection on one locus changes allele frequencies at linked loci. Results in statistical link between allele and phenotype with no mechanistic link
• Important for genetic mapping

Question 5

How can LD patterns be used to infer gene history and recent natural selection?

Answer 5

-LD decays in a predictable way at a recombination rate (r). So if current LD is known and r can be determined, it is possible to extrapolate to determine when a new mutation first occured

Question 6

What are selective sweeps?

Answer 6

Strong natural selection leading to rapid fixation of a favored allele. If it outpaces recombination then strong genetic hitchhiking can occur

Question 7

What does LD mean for understanding how natural selection operates across real genomes? What are some types of genomic structure (having to do with distribution of genes under selection) that might be driven by this relationship?

Answer 7

Critical for understanding the evolution of complex traits