18. POPULATIONS & EVOLUTION Flashcards
Define population
All the individuals of one species in one area at a time
Define gene pool
All the alleles of the genes within a population at one time
Define allele frequency
The proportion of an allele within the gene pool
What does the Hardy Weinberg principle predict?
That the frequency of alleles in a population will not change over time
Describe the five assumptions the Hardy Weinberg principle makes
There is no migration to introduce or remove alleles from the population
There are no mutations to create new alleles
There is no selection favouring particular alleles
Mating is random
The population is large
Recall both Hardy Weinberg equations
p + q = 1
p2 + 2pq + q2 = 1
What is p in the Hardy Weinberg equation?
Number of dominant alleles in the population
What does p2 stand for in the Hardy Weinberg equation?
Number of homozygous dominant genotypes in the population
What is q in the Hardy Weinberg equation?
Number of recessive alleles in the population
What does q2 stand for in the Hardy Weinberg equation?
Number of homozygous recessive genotypes in the population
What does 2pq stand for in the Hardy Weinberg equation?
Number of heterozygous genotypes in the population
How do most new alleles arise?
Mutations
What two factors cause phenotypic variation in a population?
Mutations (creating genetic variation), and environmental factors
Define what a selective pressure is
Any reason for individuals to have a survival advantage
Give examples of selective pressures
Competition for food, space, water, mates and territory. Diseases.
Natural selection will only occur if which two pre-requisites occur together
Phenotypic variation and a selection pressure
In natural selection, which individuals are more likely to reproduce more?
The individuals with the selective advantage
In natural selection, which alleles are more likely to be passed onto offspring?
The alleles that code for the phenotype with the selective advantage
What happens to the frequency of alleles in subsequent generations because of natural selection?
The alleles coding for the phenotype with the selective advantage will increase in frequency
Name the three types of natural selection
Directional, stabilising and disruptive
In directional selection, what happens to the frequency of alleles in subsequent generations?
Directional selection will increase the frequency of alleles in one direction
When will directional selection occur?
When there is a change in the environment
Why does directional selection occur?
Because one phenotypic extreme is better adapted / has a selective advantage
What happens to the modal phenotype in directional selection?
It changes in one direction