final - post midterm again Flashcards
What is a real world example of directional selection?
Warfarin resistance in mice - resistance evolved rapidly following exposure but declined rapidly after exposure because the resistant allele was not beneficial otherwise - cost of adaptation
Insecticide resistance is often based on ___ mutations of ___ ___. Resistance is usually ___
single mutations of large effect
dominant
Real example of heterozygote advantage?
sickle cell anemia
Define antagonistic selection
A source of selection opposes another source of selection on a trait
Two causes of antagonistic selection
Temporal fluctuation - fluctuating environments favour diff genotypes across generations
Spatial fluctuation - different genotypes are best adapted to diff microhabitats
Antagonistic and soft selection can lead to ____
multiple niche polymorphism - superior fitness of different genotypes to different portions of an environment - seedcrackers
Multiple niche polymorphisms are more likely to occur if each individual only experiences ___ environment
one
Define soft and hard selection
Soft - occurs when the survivors of an environment is determined by competition for a limiting factor - the RELATIVELY superior genotype has a higher survival rate
Hard - survival depends on absolute fitness not competitor density
What is inverse frequency dependent selection?
the rarer the phenotype , the greater the fitness
Why have most organisms evolved a 1:1 sex ratio?
it is an evolutionary stable strategy - selection favors individuals who produce the minority sex - increases the amount of individuals that can actually reproduce- effective population size
What is positive frequency dependent selection + examples?
the more common a phenotype the greater the fitness- muellerian mimicry - two species mimicking eachother - increased fitness
What is mutation selection balance?
Advantageous alleles should go to fixation but bad alleles can persist in population byu recurrent mutation or gene flow from another population
How do selection and drift interact?
drift doesn’t affect a population if selection is strong compared to pop size - but drift and selection can act on the same trait in the same way to move the population to a different adapted peak - a peak shift
What is the breeders equation?
R = h^2s where R is response, h2 is heritability and s is selection
What is the selection differential?
Difference between mean character in a population before and after seleciton
What is correlated selection?
some combinations of traits are favorable - garter snakes - better to be spotted and run away or striped and stand ground but not the other combinations
What are the main components of phenotypic variation?
Vg - genetic variance]
Ve - environmental variance
Difference between broad and narrow scale heritability - which do we use in the breeders equation?
broad - estimate of variance with a genetic basis - does not reflect amount transmitted between generations
narrow - estimate of variance with an additive genetic basis - does reflect amount transmitted between generations
What is one method to estimate heritability? Possible considerations?
parent offspring regression - the slope = h2 if h2 = 0 then there is no variation as there is likely only one possibility
looked at example in beak shape in finches - must be heritable
Does a resemblance between parent and offpsirng mean the trait is heritable?
Not always, could be independently determined due to environment
Two common issues with parent offspring regressions?
Maternal effects - parents provide more to offspring than genes
Environment - parent and offspring often share environments - environmental factors
What is a better way to estimate heritability?
The animal model - needs phenotypic data and pedigree to give heritability
What can genetic correlations be due to?
pleiotropy
Linkage diseq
If a trait exhibits a genetic correlation with trait 2, then evolution will depend on ______ acting on trait 1 and its _____ with trait 2
the strength of selection and association
six causes of linkage diseq?
non random mating
new mutations
union of two populations
low populations
drift
selection
What is life history?
age specific probabilities or survival and reproduction
Five traits that affect life history?
lifespan
offspring number
offspring size
generation time
breeding events
Semelparity vs iteroparity?
semelparity - an organism produces all of its offspring in a single event
iteroparity - reproduces across multiple events
Two theories behind why we age?
Mutation accumulation with age
antagonistic pleiotropy
both theories rest on the principle of a selective advantage of early reproduciton
Explain how mutations accumulate with age?
Selection will more effectively purge bad mutations affecting early life traits - therefore mutations affecting late life traits can accumulate
What are offspring quality / quantity trade offs?
You can generally produce many weak offspring or few strong offspring - negative correlation - need to consider parental survival too
Four kinds of sexual reproduction?
outcrossing - mating with another genetically distinct individual
self fertilization - union of gametes produced by the same individual
anisogamy - distinct sexes
isogamy - uniting cells are the same size
What is sequential hermaphroditism?
some organisms (fish, worms) change sex over lifespan - predicable using life history
Two kinds of asexual reproduction ?
Vegetative propagation - production of offspring from somatic tissue
Parthenogeneis - development from an egg to which there has been no contribution of genes - via apomixis where an individual develops from mitotically produced cells (not meiosis)
Pros/ cons of asexual reproduction?
its faster, dont need a partner, more reliable and takes less energy BUT there is ZERO genetic diversity which makes the species unable to adapt to change
Why is sexual reproduction preferred despite being seemingly less efficient
asexually producing species seem to have evolved from sexually producing ones
- combines new mutations or rare alleles to create potentially more fit genotypes
- can adapt to varying environments and parasites
- can separate beneficial and harmful mutations
What is mullers ratchet?
in an asexually reproducing population more fit genotypes can be lost due to drift - offspring will always carry more mutations than their parents - mutations accumulate - leads to less fitness
What is the hill robertson effect?
if a mutates to A and b mutates to B and A and B have higher fitness… without recombination A is in diseq with b and vice versa - beneficial alleles can be lost due to LD with bad alleles
Two schools of thought on species?
Nominalism - we make species up
Realism - nature is divided into species
Define horizontal and vertical species concepts?
horizontal - aim to define species at one point in time]
vertical - aim to define species across time and which individuals belong to which lineages
What is the phenetic species concept?
define species based on shared traits - phenotypes - used to be based only on looks to a wiltype but now has statistics involved
What is the biological species concept?
species are groups of potentially interbreeding populations which are reproductively isolated from other groups
What is reproductive isolation?
lack of gene exchange between species due to biological not geographic factors
What are some prezygotic isolating barriers?
ecological isolation - mates do not meet
temporal isolation - diff breeding times
habitat isolation - diff breeding locations
immigrant inviability - immigrants do not survive long enough to breed
behavioural isolation - prevents mating - assortative mating
pollinator isolation in plants
What are postmating isolation barriers?
mating occurs but zygotes are not formed
- mechanical isolation - parts dont fit
- copulatory isolation - failure to fertilize because of behaviour / stimulation
- gametic isolation
-immigrant inviability if mating occurs in a foreign habitat
What are postzygotic isolation barriers?
hybrid zygotes are formed but have less fitness
- hybrids do not have a niche
- behavioural sterility - less successful at finding mates
- developmental problems bc hybrid
- sterility for real
Primary and secondary hybrid zones?
primary - originate as geographic variation in natural selection alters allele frequencies in a continuously distributed population
secondary - formed when two previously allopatric populations that have become genetically different expand and meet and interbreed
Three stages to speciation?
population isolation - divergence - reproductive isolation (following secondary contact)
Four modes of speciation?
Allopatric speciation - geographic barrier
Peripatric speciation - founder effects
Parapatric speciation - no physical isolation but wide range
Sympatric speciation - genetic differences - no physical isolation
What is a homoplasy?
similar characteristics that have not been derived from a common ancestor
