Random Events Flashcards
What is a gonochoric (dioecious) population?
A species with two sexes
Do males or females have higher mating success?
Females
When a few founders move to a new area but keep the same genetic variation as the parental population
Founder event
Is it likely a founder event will produce homozygosity? Why?
It is not likely to produce homozygosity because as you add individuals to the founding population the chance of all being homozygous exponentially shrinks
Random change in allele frequencies between generations
Genetic drift
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How does sexual reproduction reconstruct low-load genotypes?
Through recombination and independent assortment
Does a small or large population experience more genetic drift?
Small. Large pops follow more closely to HW
A function of rate of drift and rate of mutation
Genetic polymorphism
What reduces heterozygosity and thus reduces genetic variation?
Genetic drift
The does the f value tell us?
Homozygosity. The chance of drawing two identical alleles
What is the consequence of Mullers ratchet?
Over time, the population with low fitness genotypes increases and causes a decrease in the population size as genotypes slide off the end of the scale
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How does natural selection act on the highly negative mutations?
It gets rid of them right away through purifying selection
What two ways can the founder effect occur?
- An allele is lost and another becomes more frequent
2. No alleles are lost but one allele is more frequent
What increases heterozygosity and thus increases genetic variation?
Mutation
How does migration (gene flow) violate HW?
By introducing or removing alleles from the population
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What is Mullers ratchet a disadvantage for?
Asexually reproducing individuals
What is a tornado or other natural disaster wiping out a large population of plants and effectively getting rid of a particular allele in the process an example of?
Genetic drift
What two things are needed for the march to homozygosity to be true?
- Alleles are selectively neutral
2. Evolution has occurred by a random process
What is always the eventual result of genetic drift no matter how large the population is?
Fixation. One allele being lost
Equation for heterozygosity
H = 1 - (p^2 + q^2)
How does sexual selection stop Mullers ratchet?
It allows for the ability to get rid of the bad mutations
What two things are good reasons for sexual reproduction?
- more variability
2. fewer lethals
What aspects of evolution are random? Which are non-random?
Random: mutation, genetic drift, migration (gene flow)
Non-random: natural selection
What two things are evidence that sexual reproduction is good from an evolutionary standpoint?
- Ubiquity. It is seen everywhere in most eukaryotes
- Longevity of sexual lineages compared to asexual lineages (most asexual organisms recently derived from a sexual ancestor)
Is heterozygosity related to HW? If so, how?
No
What leads to mutation meltdown and ultimately extinction?
Combined effect of Mullers ratchet and drift
How do mutations lead to Mullers ratchet?
Most mutations are neutral or slightly negative and an accumulation of these is bad
What is the founder effect an example of?
A type of population bottleneck
When can high mutation rates be advantageous?
In an uncertain environment/world
Can one allele be favored over the other in genetic drift?
No, it is random
When an environmental or other catastrophe decimates a large percentage of the population and when the population rebounds, genetic diversity is only a small subset of what existed before. Ex cheetahs
Population bottlenecks
What is the equation for homozygosity?
f = (p^2 + q^2) or f = 1 - H
How does sexual reproduction create more variability?
Novel combinations of alleles are created quickly and this is beneficial in changing environments
Establishment of a population by a few founders which carry only a small fraction of the total genetic variation of the parental population
Founder effect
What is an advantage of asexual reproduction over sexual reproduction?
All or most members of the pop can reproduce and thus reproductive output is much higher due to more individuals reproducing
What does the H value tell us?
The chance of drawing two different alleles. This is not the heterozygote frequency, a population with no heterozygotes can have heterozygosity
When does the speed of Mullers ratchet increase?
With decreasing population size
Does fixing occur slower or faster in small populations?
Faster
How does sexual reproduction create fewer lethals?
Sex hides or purges deleterious alleles, or just low fitness alleles, from the general population
Deleterious alleles will accumulate in an asexual population over time if mutations from bad back to good or neutral are rare. The number of individuals with 0 low fitness mutations will decrease from generation to generation as mutation load increases
Mullers ratchet
What do most species with two sexes have their sex ratio at?
Right around 50/50
How do mutation rates in asexually reproducing organisms and sexually reproducing organisms compare?
Sexually reproducing organisms experience mutation far less often
How does selection act in relation to drift and mutation?
May act before, during, or after in relation to them. It can further reduce genetic variation
When a population bottlenecks, what is the only way for rebound of genetic variation to occur?
Mutation or potentially movement of individuals from pops with more variation
What does migration (gene flow) ultimately cause?
Maintenance of genetic diversity in the face of natural selection or genetic drift
What is the march to homozygosity?
Theoretical idea that if drift is the only thing acting on a population, all of the alleles in the population will eventually be the same. The population drifts to homozygosity
Standard measure of genetic variation per locus of a population
Heterozygosity
Do males or females determine the reproductive output of a species?
Female
What are some examples of the founder effect?
porphyria variegata, Huntington’s disease, and polydactyl
