Multi-Locus Association Flashcards
Why can’t sites experiencing selection be considered independent of one another?
Sites experiencing selection are embedded within genes, chromosomes, and genomes, meaning that selection on one gene can affect other alleles nearby.
What would happen if loci were evolving independently?
If loci were evolving independently, knowing the allele at one locus (e.g., A) would not provide any information about the allele at another locus (e.g., B).
What is “linkage disequilibrium” and when does it occur?
Linkage disequilibrium (D) is the non-random association of alleles at two or more loci. It occurs when alleles at different loci are correlated, meaning they do not assort independently.
What are the two possible outcomes of linkage disequilibrium (D)?
Positive disequilibrium (D > 0): Alleles A and B are found together more often than expected.
Negative disequilibrium (D < 0): Alleles A and b, or a and B, are found together more often than expected.
What is the role of recombination in generating gametes with new allele combinations?
Recombination occurs during meiosis and generates non-parental gametes by crossing over, which creates new allele combinations at a rate determined by the recombination rate (r).
How does recombination affect parental and non-parental chromosome combinations?
Parental chromosome combinations are produced at a rate of 1–r, while non-parental (recombinant) chromosome combinations are produced at a rate of r.
What are the four main processes that generate linkage disequilibrium?
The four processes are:
Drift: Random changes in allele frequencies.
Mutation: New mutations appearing on particular genetic backgrounds.
Migration: Mixing of chromosomes from different populations.
Selection: Favoring of certain chromosome combinations over others.
How does drift generate linkage disequilibrium?
Drift changes the frequencies of chromosome combinations by chance, leading to non-random associations between loci.
What happens to genetic associations (D) over time without selection?
Without selection, genetic associations (linkage disequilibrium, D) decay by a factor of (1–r) each generation due to recombination.
How do linked sites contribute to finding the genetic basis of diseases?
Linked sites often show genetic associations, which can be traced in family pedigrees or populations through genome-wide association studies (GWAS), helping to locate disease-related genes.
What is genetic hitchhiking?
Genetic hitchhiking occurs when a neutral allele’s frequency changes because it is linked to another allele that is under selection.
How does selection at one locus affect another locus that is in disequilibrium with it?
Selection at one locus can cause allele frequencies at another linked locus to change due to genetic hitchhiking if the loci are in linkage disequilibrium.
What is epistasis, and how does it affect linkage disequilibrium?
Epistasis refers to interactions between the fitness effects of alleles at different loci. If epistasis is present, selection can generate and maintain linkage disequilibrium.
Can mean fitness decline due to recombination and selection? If so, how?
Yes, mean fitness can decline due to recombination breaking up favorable allele combinations, especially when both loci are under selection. This process can lead to dips in fitness before reaching equilibrium.
What are the key processes that cause linkage disequilibrium to arise?
Linkage disequilibrium arises from drift, mutation, migration, and selection.
