Selection at a single locus Flashcards
Define population genetics.
The study of variation within a population over the generations.
Define quantitative genetics.
The study of quantitative (measurable) characters and their contribution to specific phenotypes.
Where is quantitative genetics most widely used?
In selective breeding.
Define phylogenetics.
The study of long-term evolution where changes to DNA become fixed and lead to speciation.
What are the 2 main forces acting in population genetics?
- Selection
2. Stochasticity
What is meant by natural selection?
Disparities in fitness between geno/phenotypes.
What is meant by sexual selection?
Male-male competition and female mate choice.
What does stochasticity mean?
Variation.
Define genetic drift.
The chance disappearance of alleles in a small population caused when individuals die or fail to reproduce.
Does genetic drift create variation?
Yes.
Define a continuous trait.
One that can have any numerical value across an infinite scale.
What kind of distribution do continuous traits have?
Normal distribution.
Define a discontinuous trait.
One that can only fit into discrete categories.
How many loci are involved in continuous traits? What is the effect of each of these loci?
Multiple loci are involved each with a small effect on the phenotype.
How many loci are involved in discontinuous traits? What is the effect of each of these loci?
Few or a single loci is involved with a large effect on the phenotype.
Give a famous example of a population genetics study?
The peppered moth.
What is biston betularia?
The peppered moth.
What are the 2 forms of biston betularia?
Typica (white) and carbonaria (black).
Why did carbonaria become successful?
Due to industrial melanism - the black allele proved advantageous during the industrial revolution when the trees were covered with soot.
What happened to carbonaria after the Clean Air Act in 1956?
It declined.
What caused carbonaria?
A mutant dominant allele.
What is a model?
A mathematical representation used to understand a concept.
The simplest models are those with ‘non-overlapping generatins’. What kind of life cycle do these organisms have?
Birth-survival-reproduction-death.
What does ‘w’ represent?
Fitness.
What is ‘1-s’?
The selection coefficient. 1 is the average survival and ‘s’ represents the least-fit genotype.
What does w-bar stand for?
The average fitness.
How do you calculate w-bar?
It is the sum of each genotypic frequency multiplied by its fitness value.
You can work out the frequency of an allele by using genotypic frequencies. How?
The sum of all the genotypic frequencies involving that allele multiplied by their respective fitness values, divided by the average fitness of the population. E.g.
(p2 x p2w) + (pq x pqw)/w-bar
When using genotypic frequencies to work out allelic frequency, you halve 2pq. Why?
You are trying to work out the frequency of either p or q. 2pq is half p and half q, thus you halve it.
Define directional selection.
When one (extreme) phenotype is favoured by natural selection.
What does ‘h’ represent?
The dominance coefficient. It tells you which allele is dominant.
If h=0, what does that say about the fitness of 2 genotypes AA and Aa?
The fitness of AA and Aa is the same showing A is completely dominant.
If h=1, what does that say about the fitness of 2 genotypes AA and Aa?
That actually Aa and aa have the same fitness and ‘a’ is dominant instead of A.
If h=1/2, what does that say about the fitness of 2 genotypes AA and Aa?
There is no dominance between alleles.
If 0<1, what does that say about the fitness of 2 genotypes AA and Aa?
There is intermediate dominance of A and a.
If h<0, what does that say about the fitness of 2 genotypes AA and Aa?
There is over-dominance.
If h>1, what does that say about the fitness of 2 genotypes AA and Aa?
There is under-dominance.
Define intermediate dominance. What is another name for it?
Whereby both alleles contribute equally to the phenotype, also called co-dominance.
Define over-dominance.
There is an advantage to being a heterozygote.
Define under-dominance.
There is a disadvantage to being a heterozygote.
List 4 factors that affect allelic frequencies.
- Migration
- Mutation
- Sexual selection
- Reproductive success
