Populations and Speciation Flashcards
Gene Pool
All the alleles of all the genes existing at a given time.
Allelic Frequency
The number of times an allele occurs within the gene pool
Hardy-Weinberg Principle Assumptions
1) No mutations
2) Random Mating
3) Large Population
4) No selection, all alleles equally likely to be passed on
5) Isolated Populations, no flow of alleles into or out of population
Hardy-Weinberg Equations and Calculation
p + q= 1
p^2 + pq + q^2= 1
q squared is probability of recessive characteristic, then work out q and p.
Factors causing Phenotypic Variation
1) Mutation of Alleles
2) Random Fertilisation pf Gametes
3) Meiosis
4) Environmental Influence
Natural Selection Causes
Predation, disease and competition impacting ability to survival and reproduction which results in natural selection of beneficial alleles.
Natural Selection Impact on Gene Pool
Organisms with advantageous alleles more likely to survive and reproduce and pass down favourable alleles to offspring, causing frequency of unfavourable alleles to decrease
Stabilising Selection
Stable environmental conditions result in the phenotypes closest to the mean being favoured. As a result those with phenotypes closer to the mean are more likely to survive, reproduce and pass on the allele. Phenotypes towards the extreme are likely to be eliminated.
Directional Selection
A change in the environment leads to a phenotype to the left or right of the mean being best suited to survive, reproduce and pass on their alleles. As a result the mean of the population moves in the direction of the favoured phenotype.
Disruptive Selection
Opposite of stabilising selection. Both extremes are favoured over the mean and so population becomes phenotypically divided
Speciation
The genetic makeup of two populations of the same species changes so that they can no longer interbreed to produce fertile offspring
Genetic Drift
A change in a populations allelic frequency due to chance, caused by mutations.
Genetic Drift: Large vs Small Populations
Impacts small populations more as the gene pool is smaller and so there are less alleles so a mutation to one is more likely to affect the whole population for smaller populations as the allelic frequency will be higher.
Allopatric Speciation
Occurs when two populations are geographically separated by a physical barrier that prevents interbreeding, two different environments may mean different alleles are favoured which may result in natural selection influencing the two populations differently leading to two different species over hundreds of generations
Sympatric Speciation
Speciation when there is no physical barrier between populations of a species.
