Basic selection theory and the maintainance of variation
23 important questions on Basic selection theory and the maintainance of variation
What is directional selection?
s=selection coefficient
h=dominance coefficient
What is heterozygote advantage?
What is a polymorphic equilibrium
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What happens when DeltaQ is very large
- To examine this possibility, it is necessary to analyze the local stability of the equilibrium by looking at Deltaq after small perturbations of allele frequencies away from equilibrium
Natural selection can lead too...
But also to the maintenance of variation
In practice, unless selection is strong, is is difficult to...
If variants are maintained by heterozygote advantage...
What is adaptive landscape?
What is Lamarckian inheritance?
What are haploid populations?
- generations are discrete
- population size is large so genotype frequency fluctuations can be disregarded
- Fitness effects of alleles A1 and A2 are independent of fitness effects from the other side
What are the assumptions of diploid populations?
- The fitness of a genotype is proportional to its contribution of gametes to the offspring of the next generation
- No sex differences in offspring of different genotypes
- Fitness of an individual is determined solely by its own genotype
What is marginal fitness?
Stability of an equilibrium with heterozygote advantage
- To determine how stable a system is, you see how it responds to disturbances/perturbation
- Basically, when there is heterozygote advantage there is a locally stable equilibrium
- When q isn't yet at the equilibrium value it will always slowly approach q* over time
What is heterozygote disadvantage?
- This mainly occurs with respect to chromosome rearrangements as homozygotes simply have the same thing on both sides and heterozygote disturbances can occur
What is negative frequency dependence?
- Selection selects for rare phenotypes in a population and incerases a population's genetic variance
What is positive frequency-dependent selection?
With frequency dependent selection:
- The stable equilibrium does not necessarily have the highest mean fitness
- The polymorphic equilibrium is not locally stable. So not all situations will definitely drive towards the equilibrium
What is batesian mimicry?
Temporal variation in fitness...
What is projected polymorphism?
- It shows that each allele can invade a population in which the other allele is initially fixed
When can an alelle invade a population in which a different allele is fixed ?
When can polymorphisms be maintained and under which conditions?
- This can only happen under conditions of levenes model:
- Population encounters two or more niches in which all selection takes place
- The relative fitness should vary across niches
- Survivors mate randomly regardless of niche
- Each niche contributes a fixed proportion to the next generation
What is soft selection?
- With soft selection there is no relationship between the mean fitness of individuals and the contribution of a niche to the population
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