Natural Selection on SNP mutation in Haploid Bacteria & Bacteriophages
Selection in a haploid system involves a selective
advantage for one or the other of two SNP alleles
at a locus, rather than a diploid genotype.
Here, the newly arisen SNP mutation in the MS2
RNA phage gene is C206U.
[The notation indicates that the standard C base at
position 206 has mutated to a U base]. The U
allele has a selective advantage: the graph shows the
increase in frequency of the U allele at intervals
of 25 generations. The error bars show variation
in the rate of fixation among replicate cultures. The
increase in f(U) is exponential, and the pre-existing
C allele is the minority alleles in some populations
by 50 generations, eliminated in some populations by 75 and
in all by 100 generations. Contrast this to the behavior of
a disadvantageous allele in a diploid system, where
it is never entirely eliminated because when rare it show up
only in heterozygotes.
The haploid selection model accounts for the increase of the 'Delta' & 'Omicron' variants of the Covid-19 RNA virus. Whereas the example above describes a selective advantage in vitro, first the Delta and now the Omicron variants are at a selective advantage in vivo because of its higher infectivity rate (Ro, read as "R nought") relative to the original Alpha strain.
The haploid selection model accounts for the increase of the 'Delta' & 'Omicron' variants of the Covid-19 RNA virus. Whereas the example above describes a selective advantage in vitro, first the Delta and now the Omicron variants are at a selective advantage in vivo because of its higher infectivity rate (Ro, read as "R nought") relative to the original Alpha strain.
Figure © 2013 by Sinauer; Text material © 2024 by Steven M. Carr