Chapter 9 Flashcards
Staphylococcus aureus
MRSA ( methicillin resistant )
- it is a modified membrane protein that does not bind methicillin
MRSA
can have fitness costs to bacterial cell in absence of antibiotics because they are hard to eliminate
messes up cellular machinery, not as good as wild type.
without methicilin (antibiotic)
several genes affecting a system
polygenic traits
so much variation that not all genotypes are expressed
latent variation
could shift allele frequency
selection
can pull out new phenotypes without mutation
reassortment
Genes at 2 or more loci interact in nonadditive ways
Epistasis
Effects of one depend on context set by other
Phenotypic effect of loci context dependent
ex/ beach mice
-then natural selection acts on the combination of genes that produce certain phenotypes
if a favorable allele is liked to another
genetic hitchhiking
Even an unfavorable allele may increase in frequency
Genetic Linkage
Further apart genes will break this association faster
Genetic Linkage
Diversity in loci around selected locus less than neutral model
Genetic Linkage
Can work in reverse
Genetic Linkage
deleterious alleles may take good one with them
background selection
-result of genetic linkage
reduce variation
genetic linkage
Favorable gene arises in population & goes to fixation, takes everything with it
-selective sweep
-this happens in periodic selection
( process repeats )
genes in a selective sweep can be added by
tansposons and plasmids
resistant bacteria had more resistance to other antibiotics than sensitive strains
sufonamide
if two beneficial mutations are in a population
no recombination
-one will be driven out via competition
the slowing down of selection is known as
clonal interference
Pleiotropy – single gene with multiple effects on phenotype
Epistasis – a phenotypic trait is determined by complex interactions among multiple genes
Norms of reaction – a single genotype produces different phenotypes in different environments
Dominance – one allele masks the effect of another
Multiple pathways – a common phenotype may have different genetic bases.
adaptive landscapes
idea behind adaptive landscape
phenotypic space ( mophospace)
morphological values for characters
phenotypic space
Inflorescence length and leaf length
Can be more than 2 dimensions
Phenotypic space
will lead a population up a adaptive landscape peak
Just not necessarily the best one
Natural selection
can shift a population off a peak
- so small populations easier to adapt
Genetic drift
a slow walk uphil
Natural selection
Can teleport across adaptive landscapes- extreme chances like coat color
Natural selection
” different alleles have different effects”
Wright
-genotype space
Weather smooth or jagged depends on effects
Wright’s original Map
usually some resistance gene R which has some fitness cost
And C compensatory mutations that negate that cost
Antibiotic resistance
cant easily go back to rc from RC because of
circular genome
what causes variation
- genes
- environment
- developmental noise
random chance during development
developmental nose
polygenic inheritance and epistasis
genes
Phenotype equals
genetic effects plus environmental effects
P=G+E
statistical measure of variation
variance
more difference between individuals
larger variance
humans prefer
monozygotic twins
(genetic variance 0), all environmental
inbred lines
Break Genetic Variation into
- Dominance effects
- Additive effects
- Interaction effects
Narrow-sense Heritability
sum of each genes component
additive effects
epistasis
interaction effects
Fraction of total variation due to additive genetic variation
Narrow-Sense Heritability
effects the degree to which offspring resemble parent s
Narrow-Sense Heritability
the slope of a linear regression between average phenotype of the two parents and the phenotype of the offspring
Narrow-Sense Heritability
Tendency of birds to be restless at night when it is time to migrate
Migratory Restlessness
narrow sense heritability
Often jump in the direction they want to go
Migratory Restlessness
migratory behavior is
heritable- very strongly
Difference between mean of successful individuals and all individuals
selection differential
Difference between mean value of offspring and mean of parents
selection response
allows prediction of selection
breeders equation
Began in 1996
Except 3 yrs in WWII
Illinois Long-Term Selection Experiment: Corn
Severe truncation experiment
Only top 20% and lowest 20% for oil content allowed to breed
Illinois Long-Term Selection Experiment: Corn
declines with time
Some sources of variation are exhausted
Still above 0 after 100 yrs!
Heritability
Far more variation revealed than in initial population (green)
Latent variation
as selection drives a population in directions
new allele combinations form- Latent Variation
- This has the capability of a population with a mean value that is greater than the original extent of variation
- Without any mutations taking place
Latent Variation
Darwin started the Origin of Species with what?
artificial selection
Shows the capabilities of natural populations
-Think Wolves to Dogs, Wild mustard to cabbage, broccoli, cauliflower, kale, and Kohlrabi
Latent Variation
- Experiments on bristle number in Drosophila
- Chose top 50 flies for bristle number and bred them
- Increased beyond original range of variation
- Different populations changed at different rates
- !!But all reached a plateau
Latent Variation
- !!When selection was terminated, bristle number decreased,
- Why didn’t it go higher?
- The genes were correlated with recessive lethal alleles that were increasing along with bristle number
Genetic Hitchhikers
- Latent Variation
