Populations and evolution Flashcards
What does the Hardy-Weinburg principle predict?
The proportion of dominant and recessive alleles will remain the same from one generation to the next.
What are the 5 conditions required for the Hardy-Weinberg theory to work?
- No mutations occur
- The population is isolated
- No selection occurs
- There is a large population
- mating between individuals is random
Define a gene pool
All of the alleles of all of the genes of all of the individuals in a population at a given time.
What is meant by allelic frequency?
The number of times an allele occurs within the gene pool.
What are the two equations in the Hardy-Weinberg principle?
p+q=1
p^2+2pq+q^2=1
What does p represent?
The dominant allele
What does q represent?
The recessive allele.
What genetic factors can cause variation in phenotypes?
mutations, meiosis and random fertilisation of gametes.
What is a selection pressure?
An environmental factor which can limit the population of a species.
Why must organisms produce more offspring than can be supported by the environment?
Over production ensures that there is competition between organisms resulting in differential reproduction.
What is the advantage of genetic variation?
Some individuals will have the combination of genes needed to survive.
What is stabalising selection?
Selection which preserves the average phenotype by favouring average individuals and selecting against the extreme phenotypes.
What is directional selection?
Selection which changes the phenotypes of a population by faviouring the phenotypes that vary in one direction from the mean. Selecting for the extreme phenotypes.
What is disruptive selection?
Selection that favours individuals with extreme phenotypes when an environmental factor takes on two or more distinct forms. Most important in evolutionary change.
What is speciation?
The evolution of new species from existing ones.
What is a species?
A group of individuals that have a common ancestry and are capable of breeding to produce fertile offspring. They are reproductively separated from other species.
What is allopatric speciation?
When 2 populations are geographically isolated and the environmental conditions are different in each isolated area.
What is sympatric speciation?
when 2 populations are reproductively separated in the same area.
Where can genetic drift take place?
In small populations
What is genetic drift?
In a small population, those alleles that are passed on will quickly affect the population as their frequency is high. The effect will be more rapid and they are more likely to develop into a new species.
Within each subspecies there is a range of phenotypes. Explain the factors that give rise to this variation.
Mutation produces new alleles
Phenotype depends on the environment/selection pressures.
Why may the frequency of a species remain the same for many generations?
If there is no migration and the selection pressures stay the same.
Explain why correlation does not mean causation?
There may be another factor.
Give two possible causes f variation that result from mitosis during gamete formation?
Crossing over and continuous variation
Other than DNA base sequence, give two types of evidence that can be used to determine evolutionary relationships
Anatomy/physical differences and biochemistry