Mt2 Flashcards
What is a big source of fitness variation?
Deleterious mutations
What mutations are enriched amongst the rarest alleles in the R species
Loss of function mutations- selection should depress the frequency
Heterozygote advantage/overdominance
Heterozygote has highest fitness; heterozygote could be unflavored where disease is not prevalent; result in stable/protected polymorphism; will inevitably maintain both alleles
Negative frequency dependent selection
Fitness is negatively correlated with frequency (fitness goes down as it becomes more common); rare genotypes are favored by NS; frequency increases then its not rare anymore
Self incompatibility
Method to reduce self-fertilization/inbreeding; allergic variation at S-locus
Spatially varying selection
Fitness of a phenotype or genotype will vary depending on where it is in some geographic region
Sperm are…
- less energetically expensive than eggs
- made in much greater numbers
SO a male’s fitness may be greatly increased as the number of matings increases
FEMALE MAY SUFFER reduced fitness if she mates with lower quality male
Sexual selection is…
A kind of NS (component of); male variance in mating success is often very high
Male fitness
Correlated with the number of MATES that a male has
Sexually selected trait properties
- restricted to one sex
- appear only at sexual maturity
- may only be present during breeding season
NS and Sexual selection; maximized fitness
Selection favors mating displays that maximize a male’s lifetime fitness; may be a compromise between what maximizes survival and what maximize mating success
Where do female preferences come from?
May evolve preference due to direct or indirect benefits; ex. high quality territories
Sexual selection on male biology
Male genitalia have elaborate morphology; one of the traits that evolves the fastest
“Good genes”
Indirect benefit ex.
- females should evolves preferences for male traits that are correlated with high genetic quality
- predicts that male traits are COSTLY and thus “honest indicators” of male quality
- predicts that males preferred by females should sire higher quality offspring
Runaway sexual selection
As individuals with the preferred trait are more likely to mate and pass on their genes, the trait becomes increasingly common in the population, even if it may be impractical or even detrimental in terms of survival. male traits could become so extreme that natural selection pushes back
Feedback loop and female preference
female that are expressing preferences for more and more exaggerated traits are mating with males who have those traits
Inbreeding effect on populations that experienced sexual selection
Not go extinct as quickly; more intense sexual selection has EXPOSED DELETERIOUS mutations that aren’t exposed when its not present; more chances for these mutations to be erased
Do traits evolve for the good
Not always expected to evolve for the good
Group selection
Trait occurs and the expression of it is bad for the individual, but good for others in the species
Williams idea
if you have a population composed entirely of selfish individuals it will give rise give right to a population composed of selfish individuals and may go extinct
In group selection…
Group heritability is likely low
More birth/death of individuals than groups per unit time
Kin selection
An apparently altruistic act is associated with a fitness cost to the actor and a fitness benefit to the recipient
Hamilton’s rule for when altruistic traits will evolve
Rb>c
R=degree of relatedness between actor and recipient
B=benefit to recipient
C=cost to actor
Species selection
differential survival and proliferation of entire species based on their characteristics and traits, rather than just individual organisms within those species. It operates on a similar principle to natural selection but operates at a higher level of biological organization.
Advantage of asexuality
- Asexual females will quickly replace sexual females
- An allele that suppresses meiosis will be transmitted to ALL OFFSPRING rather than just half
- An asexual female passes on all of her genes to each offspring rather than only half her genes
Does asexual taxa last
Appear to arise frequently (in some organisms) but do not appear to persist for very long
What does asexual reproduction slow down
Slows down adaptive evolution and leads to higher probabilities of extinction
How is recombination better
Sex can increase the efficiency of all kinds of natural selection; spread of beneficial mutations and the removal of deleterious mutations; increases rate at which adaptive evolution can occur
Muller’s ratchet
With no recombination, deleterious mutations can accumulate over generations, leading to a genetic load- continue to carry harmful mutations
Individual selection arguments for maintenance of sex
- G.C Williams balance argument : there must be genetic variation for suppressed sex. Given major advantage for asexuality we would expect asexuality to fix. Since sex continues, sex must have a short-term advantage.
- Sib competition
- Lottery model- asexuals can only succeed in narrowly defined niches (in unpredictable environments, producing the diverse group of offspring genotypes could be beneficial)
Sib competition model
asexual females produce clones of themselves, so all daughters have the same genotype and competing for each other for resources; better to have diff genotypes so that they aren’t competing with eachother
Lottery model
Maybe better to produce an array of different offspring genotypes because maybe one of the genotypes will be better suited to fit the change in environment that is probably going to be different from the mother’s environment
Unpredictable environment, more likely to get lucky that a variation will work
Red queen hypothesis
Host and parasite are tracking each other
Host has to adapt as quick as possible to stay in same place
Host evolving immune system to keep up with rapidly evolving parasites
Sexual female fitness is usually higher than in asexual females
Frequency of new allele in N haploids
1/N
Genetic drift
Genotypic variation is neutral; theory applies primarily to molecular data; not a result of natural selection; WHAT HAPPENS IN ONE GENERATION HAS NO EFFECT ON THE NEXT GENERATION
Are fluctuations larger in smaller or larger populations
Larger in smaller populations; pq/2N
How is heterozygosity lost in populations
Lost faster in smaller populations; rate of loss is 1/2N per generation
What is the fixation probability
0.5= starting frequency
Frequency of brand new allele
1/2N
Expected time to fix
4N generations
Allele frequency movement in large populations
Dont move around very much from one generation to the next
Genetic variation
Diversity of alleles and genotypes within a population
Drift results in…
The accumulation of genetic differences among populations
Effective population size
Describes the rate at which drift would occur in a population of size Ne
If N fluctuates over T generations
1/Ne
Effect of population bottlenecks on polymorphism
Rare alleles likely to be lost; heterozygosity may be reduced
Mutation-drift equilibrium
Rate at which variation lost by drift= neutral variation introduced by mutation
Randomly selected pair of alleles
Expected coalescent time is 2N generations
Coalescent time
Time it takes for two randomly chosen alleles in a population to converge to a common ancestral allele
Neutral theory of molecular evolution
Most new mutations are deleterious
Most observed molecular variation is neutral
Rate of evolution between species is equivalent to neutral mutation rate
The neutral mutation rate is a reflection of functional constraint
Polymorphism is a transient phase of divergence between species
Neutral theory of molecular evolution; frequency of new mutation
1/2Ne
Neutral theory; total # new mutations
2 Ne u
Why are most new mutations in proteins deleterious; explained by drift
Deleterious more common than beneficial, and under weak selection pressure, genetic drift can allow them to persist and accumulate
If there is no polymorphism
There is no evolution
There are less new mutations in smaller populations but
Each has a higher probability of fixing
Functional constraint
amino acid at that residue is critical to function
Heterozygosity
2NeU
Higher mutation rate
Greater rate of divergence between species; more polymorphism
Pseudogene
gene copies that are dead- become nonfunctional
derived from real genes
looking for something that is under no functional constraint? Prob look at pseudogenes
Evolving at ACTUAL underlying mutation rate
“Free of constraint”
No selection acting on them
Why do some proteins evolve faster than others?
Functional constraint
adaptive evolution
How is translation affected by codons matching rare tRNAs
Leads to slower translation
