7.2-3 Populations, Evolution and Selection Flashcards
What is a population?
A group of organisms of the same species
In a particular space at a particular time that can potentially interbreed
What is a gene pool?
The total number of alleles present in a population
What is allelic frequency?
The proportion if a certain allele in a gene pool
What is the Hardy-weinberg equation used for?
To estimate the frequency of alleles in a population
To see whether a change in allelic frequency is occurring
What does the Hardy-Weinberg principle predict?
The proportion of dominant and recessive alleles in a population remain constant
From one generation to the next
What is assumed in the Hardy-weinberg equation?
No mutations occur
No movement of alleles - population is isolated
Large breeding population
All alleles have an equal chance to be passed on to the next generation (no selection)
Mating is random
What are the formulas for the Hardy-weinberg principle?
p + q = 1.0
And
p^2 + 2pq + q^2 = 1
What do the p’s and q’s represent in the Hardy-weinberg equations?
p = frequency of the dominant allele (eg A)
q = frequency of the recessive allele (eg a)
p^2 = frequency of homozygous dominant (eg AA)
2pq = frequency of heterozygous (eg Aa)
q^2 = frequency of homozygous recessive (eg aa)
Why are there variations in alleles of genes?
Random fertilisation
Meiosis
Mutation
Environmental influences
What is the niche of a species?
It’s role within the environment
Therefore species with the same niche compete with each other to survive
What is the idea of natural selection?
The better adapted species survive
What has Darwin suggested about large numbers of offspring?
So there is greater intraspecific competition
So only the best alleles survive, to reproduce and pass on to the next generation
What is best in a changing environment?
Variation in genotypes and phenotypes increases the chance a species will survive
What do you include in natural selection?
Variation Mutation Environmental change Competition Survival Reproduction Alleles
(Frequency of alleles changing leads to evolution)
What is selection?
Choosing the individuals that are better adapted to their environment are more likely to survive and breed
What are the types of selection?
Directional
Stabilising
Disruptive
What is directional selection?
Selection that favours a phenotype best suited to a changing environment at one extreme of the population
This results in changes to the characteristics of a population as these individuals are more likely to survive and breed - pass on their alleles
The ‘mean’ will therefore shift
What is stabilising selection?
Selection against both extremes (eliminating extreme phenotypes) associated with non-changing/stable environments over many years
Those closest to the mean are more likely to pass their alleles on - maintaining favourable characteristics = a successful species
The range and distribution becomes smaller and narrower
What is disruptive selection?
Both extremes of the normal distribution are favoured over the mean
What is speciation?
New species arise after a population becomes separated and cannot interbreed
What are the two type of speciation?
Allopatric - caused by a physical barrier
Sympatric - chromosomal error
Describe allopatric speciation?
A population is geographically separated
Genetic variation
Natural selection leads to the frequency of alleles have changed
The two populations are so different they can’t successfully breed
= separate species
What is one other way evolution occurs? Who does this greatly affect?
Genetic drift
Chance dictates which alleles are passed on
Greatly affects a small population
Describe sympatric speciation?
A species inhabits the same geographical region
But due to a chromosomal error during cell division it could lead to reproductive isolation
Eg mechanically (penis doesn’t fit the vagina) Or courtship behaviour is no longer recognised
