Ch09-
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The evolution of resistance may incur a cost. Is resistance evolution reversible if antibiotics are not being used?
yes, but not always
Why do bacteria with resistance to antibiotics still survive although antibiotics are not in use or lessened?
they gain an allele that compensate the cost of resistant that arised from a compensatory mutation
define additive genetic effects
when a phenotype of a individual is determined by the sum of the effects of each alleles it has
define latent variation
possible genotypes/phenotypes among a large variation that are not represented in a population
why is latent variation important?
in the absent of mutation, new phenotypes can still arise from latent variation by selection & genetic reassortment
define epistasis
when two loci influence a character by influencing each other
define haplotypes
a set of alleles, one at each locus under consideration
why do we need to keep tract of the alleles and haplotypes frequencies to treat the population genetics of multiple loci
because allele frequencies are not solely responsible for haplotype frequencies, linkage is too
define Linkage disequilibrium
A statistical bias in the association of alleles corresponding to different loci
what can produce Linkage disequilibrium?
from a mutation, natural selection only when the loci are epistasis, migration, & genetic drift
when a linkage disequilibrium is present in a population, what happens to it in the absence of other evolutionary processes?
it dissipates by recombination
how can new haplotypes be generated?
by the recombination of two heterozygotes
what happens when 4 haplotypes exist in a population & recombination is absent?
• no haplotypes are produced - genotype & linkage disequilibrium is unchanged
what happens when 4 haplotypes exist in a population & recombination is present?
• haplotypes are produced, decreasing frequency of previous existing haplotype • coupling heterozygotes decreases as new genotypes appears
what are the consequences of genetic linkage?
genetic hitchhiking & background selection
in what case is genetic hitchhiking not harmful?
periodic selection in haploid organism
ultimately how do bacterial resistance to antibiotics that have been withdrawn from general use still persist?
due to periodic selection. since bacterial genome acts as a single haplotype, each new arising beneficial mutations are sweep into fixation carrying all other alleles