CGP Populations

Question 1

Define species.

Answer 1

A group of similar organisms that reproduce to give fertile offspring

Question 2

Define population.

Answer 2

A group of organisms of the same species living in the same place at the same time - so have the potential to interbreed.

Question 3

Define gene pool

Answer 3

The complete range of alleles present in a population.

Question 4

Define allele frequency.

Answer 4

How often an allele occurs in a population.

Question 5

The Hardy-Weinberg principle is only true under certain conditions which are…

Answer 5

It has to be a large population where there’s no immigration, emigration, mutations or natural selection.

There also needs to be random mating - all possible genotype to breed with all others.

Question 6

What can the Hardy-Weinberg principle be used to predict?

Answer 6

Allele frequency

Genotype and phenotype frequency

Question 7

What is the HW equation for predicting allele frequency?

Answer 7

P + Q = 1

P = frequency of one allele (usually dominant)
Q = frequent of other allele (usually recessive)

Question 8

What is the Hardy-Weinberg for predicting genotype and phenotype?

Answer 8

p2 + 2pq + q2 = 1

p2 = frequency of homozygous dominant genotype
2pq = frequency of heterozygous genotype
q2 = frequency of recessive genotype

Question 9

What is variation?

Answer 9

Differences that exist between individuals.

Question 10

What is the main source of genetic variation?

Answer 10

Mutation. But also because of differences in the environment.

Question 11

What is evolution?

Answer 11

A change in allele frequency over time.

Question 12

Outline natural selection.

Answer 12

1. Individuals of the same species vary due to different alleles. Predation, disease and competition (selection pressures) creates struggle for survival.
2. Some are better adapted for these.
3. This means there are different levels of survival and reproductive success in a population. Individuals with a phenotype that increases their chance of survival are more likely to survive, reproduce and pass on their genes than individuals with a different phenotype.
4. This means that a greater proportion of the next generation inherit the beneficial alleles.
5. They, in turn are more likely to survive, reproduce and pass on their genes.
6. So the frequency of the beneficial alleles in the gene pool increases from generation to generation.

Question 13

What are the two types of natural selection that affect allele frequency?

Answer 13

Stabilising selection, directional selection and disruptive selection.

Question 14

Define stabilising selection.

Answer 14

Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce.

Question 15

When does stabilising selection occur?

Answer 15

When the environment isn’t changing, and it reduces the range of phenotypes.

Question 16

What is directional selection?

Answer 16

Where individuals with alleles for a single extreme phenotype are more likely to survive and reproduce.

Question 17

What is disruptive selection?

Answer 17

Where individuals with alleles for extreme phenotype at either end of the range are more likely to survive and reproduce.

Question 18

When does directional selection occur?

Answer 18

Possibly in response to an environmental change.

Question 19

When does disruptive secretion occur?

Answer 19

When he environment favours more than one phenotype.

Question 20

Define habitat.

Answer 20

The place where an organism lives.

Question 21

Define ecosystem.

Answer 21

A community, plus all non living (abiotic) conditions in the area in which it lives.

Question 22

Define abiotic conditions.

Answer 22

The non living features of the ecosystem eg temperature.

Question 23

Define biotic conditions.

Answer 23

The living features of the ecosystem eg predators.

Question 24

Define niche.

Answer 24

The role of a species within its habitat eg what it eats.

Question 25

Define adaptation.

Answer 25

A feature that members of the same species have that increased their chances of survival and reproduction.

Question 26

How many species can a niche be occupied by?

Answer 26

Only one. Every species has its own unique niche.

Question 27

What happens if two species occupy the same niche?

Answer 27

They will compete with each other. One species will be more successful than the other, until only one species is left.