Presentation Detail

Population Genetics and/or Genomics, Empirical

Assaf, Zoe June [1], Petrov, Dmitri [2].

Recessive mutations interfere with selective sweeps.

The dynamics of deleterious alleles during a selective sweep have previously been explored in the context of 'hitchhiking', where a beneficial allele drags a mildly deleterious allele to fixation. This process has only been studied in the context of mildly deleterious mutations, because strongly deleterious mutations are assumed to dominate the process and thus terminate the selective sweep. However, this omission of strongly deleterious mutations is an artifact of the assumed dominance relationships between the two linked alleles. When one allows the deleterious mutation to be less dominant than the adaptive allele, then strongly deleterious mutations can indeed begin to hitchhike during the selective sweep. We use analytic approximations and a Wright-Fisher forward simulation to model hitchhiking of recessive deleterious mutations. The results show that if an adaptive allele is genetically linked to a recessive mutation, the trajectory of that adaptive allele dramatically changes. As the sweep progresses the recessive deleterious mutations become present in homozygotes at a higher and higher rate, causing the sweep to slow down and eventually stop entirely at an intermediate frequency. The combination of a recessive deleterious and a dominant adaptive allele gives rise to balancing selection via associative overdominance. After a period of time recombination can uncouple the two alleles, allowing the adaptive allele to proceed to fixation. We call this process a 'staggered sweep' and argue that this situation should be common given that the majority of strongly deleterious mutations are partly or entirely recessive. This phenomenon has direct implications for the rate and process of adaptation. We specifically focus on the effect in small populations, in experimental evolutions, and on the genomic signature of selection.

1 - Stanford University, Genetics, Department Of Genetics, Stanford University, Stanford , CA, 94305, USA
2 - Stanford University, Biology, Department of Biology, Stanford University, Stanford, CA, 94305, USa

Keywords:
Associative Overdominance
balancing selection
Recessive Mutations
inbreeding depression.

Presentation Type: Regular Oral Presentation
Session: 53
Location: Alpine A and B/Snowbird Center
Date: Sunday, June 23rd, 2013
Time: 9:45 AM
Number: 53006
Abstract ID:983
Candidate for Awards:W.D. Hamilton Award for Outstanding Student Presentation