Variation and Evolution Flashcards
What factors produce variation between individuals?
What factors produce variation between individuals? Both genetic and environmental factors produce variation.
Name the types of variation.
Continuous and discontinuous
Heritable and non-heritable
What is discontinuous variation?
Type of variation that can be categorised e.g. blood group
A characteristic can only appear in discrete values
It is influenced by one or two genes and environmental factors have little effect
What is continuous variation?
Type of variation that cannot categorised e.g. height. Produces a continuous range in which a characteristic can take any value. It is influenced by multiple genes and is often significantly affected by environmental factors
Compare heritable and non-heritable variation.
Heritable variation is the genetic differences between individuals whereas non-heritable
variation is acquired differences in the phenotypes of individuals that cannot be inherited.
What is evolution?
The change in allele frequencies in a gene pool of a population over time.
How does natural selection cause a change in allele frequencies over generations?
Organisms with advantageous characteristics are more likely to survive and pass their favourable alleles to offspring. Frequency of unfavourable alleles decreases.
What are selection pressures?
Environmental factors that drive evolution by natural selection and limit population sizes. They can change the frequency of alleles in a population
Give examples of selection pressures.
- Predation
- Disease
- Competition (for food, habitats, mates)
- Environmental conditions, e.g. temperature
How can allele frequencies be expressed?
Expressed as a percentage or proportion of the total number of all alleles for that
gene.
State the two types of competition.
Interspecific
Intraspecific
What is interspecific competition?
A type of competition that takes place between members of different species.
What is intraspecific competition?
A type of competition that takes place between members of the same species.
Define gene pool
All of the different versions of genes (alleles) in the individuals that make up a population.
What is genetic drift?
Variations in allele frequencies in small populations due to chance (rather than as a result of selection pressures).
What is meant by the founder effect?
When a small number of individuals become isolated, forming a new population with a limited gene pool. Allele frequencies are not reflective of the original population.
What is the Hardy-Weinberg principle?
A model that allows the estimation of the frequency of alleles in a population, as well as whether allele frequency is changing over time.
State the assumptions made by the Hardy-Weinberg principle.
- No mutations occur to create new alleles
- No migration in or out of the population
- No selection, alleles are all equally passed on to the next generation
- Random mating
- Large population
Explain the Hardy-Weinberg equation for calculating allele frequency.
The frequencies of each allele for a characteristic must add up to 1.0 giving the equation: p + q = 1.0
Where p = frequency of the dominant allele, and q = frequency of the recessive allele
Explain the Hardy-Weinberg equation for calculating genotype frequency.
The frequencies of each genotype for a characteristic must add up to 1.0 giving the equation: p2 + 2pq + q2 = 1.0
where p2 = frequency of homozygous dominant, 2pq = frequency of heterozygous, and q2 = frequency of homozygous recessive
Define speciation.
The formation of new species due to the evolution of two reproductively separated populations.
Why may speciation occur?
Genetic drift in isolated population
Founder effect
Natural selection
What are the two types of speciation?
- Allopatric speciation
- Sympatric speciation
What is the term for speciation that occurs when two populations become geographically isolated?
Allopatric speciation
