Chapter 18 - Populations and Evolution

Question 1

What is a “population”?

Answer 1

A population is a group of organsims of the same species living in the same area at the same time, who have the potential to interbreed

Question 2

What is a gene pool?

Answer 2

A gene pool is all of the different alleles of all of the different genes amongst all the members present at any one time

Question 3

What is allele frequency?

Answer 3

Allele frequency is how often each allele occurs within a gene pool

Question 4

What does the Hardy-Weinberg mathematically show?

Answer 4

Allele frequency does not change between different generations of the same population

Question 5

What conditions must be met for Hardy-Weinberg to be true? (5)

Answer 5

No mutations occur between the generations
The population is isolated (no unexpected gain or loss of alleles)
No selection pressures are applied on the population
Mating is random in the population
It is a large population

Question 6

Which two Hardy-Weinberg equations allow you to calculate the phenotype, genotype and allelic frequency within a population

Answer 6

p + q = 1
P^2 + 2pq + q^2 = 1 , where p^2 is homozygous dominant

Question 7

Why may phenotypes vary widely in populations? What causes this variation?

Answer 7

Different genetic and environmental factors are able to influence phenotypes, and they are caused by different genotypes and the mutations to them. The second largest cause of variation within a population is meiosis during reproduction

Question 8

What three main factors result in differing levels of survival and reproduction among populations?

Answer 8

Predation, disease and competition (i.e natural selection)

Question 9

What is the concept of natural selection?

Answer 9

Those within a population who have phenotypes more suited to survival (resistance to disease and predation, outcompetes peers) are more likely to survive and pass their genes onto their offspring, resulting in a change in allele freuqency in a gene pool

Question 10

What is stabilising selection?

Answer 10

Stabilising selection is where selection pressures are applied to a population which suit the mean phenotype of a population more than the extremes, resulting in a decrease of the periphary phenotypes and an increase in the number of mean phenotypes

Question 11

What is directional selection?

Answer 11

Directional selection is where a selection pressure is applied to a population which prefers one extreme of the phenotype, and the other extreme is selected against. This causes the allele frequency in the population to shift towards whatever side is favourable

Question 12

What is disruptive selection?

Answer 12

Disruptive selection is where both extremes are favoured, but the mean phenotype is not favoured, so phenotypes of both extremes increase whilst the mean decreases, eventually leading to new species being created

Question 13

What is the definition of evolution of a population?

Answer 13

The change of allele frequency in a population

Question 14

What is allopatric speciation?

Answer 14

Where geographical seperation occurs within one population forming two, resulting in an accumulation of differences within their gene pools. When the two populations are no longer able to breed with one another to produce fertile offspring, they are now new, different species

Question 15

What is sympatric speciation?

Answer 15

Sympatric speciation refers to any other sort of reproductive isolation which is not geographic, such as mutations to genes which control courtship behaviour, or a new species or loss of an old species which is important in the reproduction of a species, leading to two genetically distinct species

Question 16

What is gene drift and why is it important, particularly in small populations?

Answer 16

Gene drift mostly affects small populations, and when they reproduce whatever gene they pass on will have a larger affect on allele frequency than it would in a larger population, especially if there is a smaller gene pool. This means that if a mutation occurs within a small population it can quickly create a new species due to how quickly it can affect allele frequency, which is favourable because it can protect small populations, which tend to have little genetic diversity and small gene pools, agaisnt new selection pressures which would otherwise wipe them out