Variation And Evolution Flashcards
Define species
A population of organisms similar enough to breed and produce fertile young
Genetic Drift
A change in allele frequency because of chance, more likely in small populations
Define The founder effect
When a small population has become separated from the original population and so an allele in the small population becomes more frequent in the succeeding generations
Define Speciation
Allele changes can significantly alter the phenotype of the isolated population so they can no longer breed with the original population to give fertile young. A new species has been formed
Define Variation
The phenotypic differences between members of the same species
What is heritable variation?
Can be passed on to offspring
Genetic differences caused by crossing over, independent assortment and sexual reproduction
What is non-heritable variation
Cannot be passed onto offspring
Genetic differences caused by the environment
What is discontinuous variation?
- Type of variation that can be categorised e.g. blood group
- A characteristic can only appear in discrete values and no intermediates
- Monogenic
- Gene expression not influenced by the environment
What is continuous variation?
- Type of variation that cannot be categorised e.g. height
- Produces a continuous range in which a characteristics can take any value
- Gene expression is influenced by the environment and forms a normal distribution curve
How does natural selection cause a change in allele frequency over generations ?
Organisms with advantageous characteristics are more likely to survive and pass their favourable alleles to offspring. Frequency of unfavourable alleles decrease.
What is a selection pressure ?
- Environmental factors hat drive evolution by natural selection and limit population size
Pass successful alleles into next generations
E.g Predation, Disease, Competition and Environmental Conditions
What is intraspecific competition?
Competition between members of the same species
What is interspecific competition?
Competition between members of different species
Define gene pool
All the alleles of all the genes of all the individuals in a population of sexually reproducing organisms
What is genetic drift?
The change in allele frequency in a population by chance (rather than selection pressures)
This is most significant in small or isolated populations
What is the Hardy- Weinberg Principle ?
An equation that estimates the allele frequency in a population, as well as whether it is changing over time
What assumptions are made by the Hardy-Weinberg Principle?
- No migration
-No mutation
-No selection pressure - Large population
Give and explain the Hardy Weinberg Equation
p2 + 2pq + q2 = 1
P= frequency of dominant alleles
q = Reccesive allele
p+q = 1
P2 = Frequency of homozygous dominant
2pq= Frequency of heterozygous
q2 = Frequency of homozygous recessive
What are the 2 types of speciation ?
Allopatric and Sympatric
What is allopatric speciation?
Caused by physical barriers (geographical isolation) . As the 2 groups become separated and reproductively isolated as a result, the gene flow is reduced
What is sympatric speciation?
Evolution of a new species from demes sharing the same geographical location
This can cause morphological isolation (the genitalia become incompatible and cannot breed) and also
Behavioural Isolation (differing rituals will not interbreed and become isolated)
Outline geographical isolation
A physical barrier (such as rivers or mountains ) separates 2 populations of the same species
What are the potential isolation mechanisms in sympatric speciation ?
Morphological isolation
Seasonal isolation
Behavioural isolation
Gametic isolation
Hybrid Sterility
Hybrid in viability
What is seasonal isolation?
Deemed with different breeding seasons cannot interbreed and become isolated
What is hybrid sterility?
When two different species are similar enough to bred, they can produce offspring but these are often sterile and unable to breed themselves
Could be due to an uneven chromosome number which cannot form homologous pairs
What is hybrid fertility
Some plants can double their chromosome number by endomitosis to become fertile
Selection pressure for vs against
For
- Phenotypes have an advantage in competition so the alleles that code for them are selected for
Against
-Phenotypes do not have an advantage and are unable to compete successfully. So alleles. That code for them are selected against
