Chapter 20 - Patterns of Inheritance and Variation Flashcards
What is the Hardy-Weinberg principle?
In a stable, non-evolving population, allele frequencies stay constant
What assumptions are made in the Hardy-Weinberg principle?
- Large population size
- Random mating
- No mutations
- No selection pressure so no evolution
- No gene flow
In the Hardy-Weinberg principle, what letter are dominant alleles represented by?
p
In the Hardy-Weinberg principle, what letter are recessive alleles represented by?
q
What is the equation for the Hardy-Weinberg principle?
p^2 + 2pq + q^2 = 1
What does p + q always equal in the Hardy-Weinberg principle?
p + q = 1
You can use this to work out what p or q is when you are given only one of the values
What is the gene pool?
The sum total of all the genes in a population
What is allele frequency?
The relative frequency of a particular allele in a population
In what situations would the Hardy-Weinberg principle not apply?
In any population in which any one of the assumptions of the Hardy-Weinberg principle are not met e.g. small population, gene flow occurring
What different factors affect evolution?
Mutation
Changes in population size
Genetic drift
Selection of favourable alleles
How does mutation affect evolution?
Mutation leads to genetic variation, in which favourable alleles can be selected
What are the two different types of factors affecting population size?
- Density dependent factors
- Density independent factors
What are density dependent factors?
Factors dependent on population size e.g. competition, predation
What are density independent factors?
Factors independent of population size e.g. climate change, natural disaster
What are small changes in population often caused by and what do they lead to?
They are often caused by migration, and can lead to gene flow
What is gene flow?
The movement of alleles between populations resulting in changes in allele frequency
What can large changes in population lead to?
Genetic bottleneck
What is a genetic bottleneck?
Where there is a reduction in population size that lasts for at least one generation, and results in a greatly reduced gene pool and genetic diversity
Where does genetic drift most commonly occur?
In small populations
What is genetic drift?
The impact of changes in alleles due to random mutation
What is an extreme example of genetic drift?
The founder effect
What is the founders effect?
Where an new population is established by a small number of individuals from a larger population, leading to the formation of population with a lack of genetic diversity and variation
What are the two types of selection of favourable alleles?
Sexual selection
Natural selection
What is sexual selection?
Alleles that promote mating success are selected
What is natural selection?
Alleles that promote survival success are selected
What are the 3 types of natural selection?
Stabilising selection
Directional selection
Disruptive selection
What is stabilising selection?
Where the norm or average is selected for and the extremes are selected against (peak in middle)
What is directional selection?
Where a new selection pressure causes the more common phenotype to no longer be the most advantageous, meaning there is a shift in allele frequency towards one previous extreme/rare phenotype (shift in peak to one extreme)
What is disruptive selection?
Where the extremes are selected for and the norm selected against (shift in peak to both extremes)
