Population And Evolution

Question 1

Define species

Answer 1

A group of organisms that can interbreed to produce fertile offspring

Question 2

Define population

Answer 2

All the organisms of a particular species that live in the same place

Question 3

Define gene pool

Answer 3

The range of different alleles existing for a particular locus within a population

Question 4

Define allele frequency

Answer 4

The proportion of a certain allele within a gene pool, expressed as a decimal or percentage

Question 5

What is the Hardy-Weinberg principle?

Answer 5

Allows us to estimate the frequency of alleles in a population as well as if allele frequency is changing over time

Question 6

Give the 5 assumptions made by the Hardy-Weinberg principle

Answer 6

No mutations occur to produce new alleles

No migration in or out of a population

No selection

Random mating

Large population

Question 7

Explain the Hardy-Weinberg equation for calculating allele frequency

Answer 7

The frequencies of each allele for a characteristic must add up to 1. The equation is therefore p+q = 1 where p = frequency of dominant allele and q = frequency of recessive allele

Question 8

Explain the Hardy-Weinberg equation for calculating genotype frequency

Answer 8

The frequencies of each genotype for a characteristics must add up to 1. The equation is therefore p2 + 2pq + q2 = 1

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

Question 9

Give genetic factors that cause phenotypic variation within a species

Answer 9

1. Mutation of alleles
2. Random fertilisation by gametes
3. Random assortment of genetic material during meiosis

Question 10

Other than genetic factors, why else may phenotype vary within a species?

Answer 10

Environmental influences

Question 11

Why does natural selection occur?

Answer 11

Predation
Disease
Competition

All resulting in differential survival and reproduction

Question 12

How does natural selection cause a change in a populations gene pool over generations?

Answer 12

Organisms with advantageous characteristics are more likely to survive and pass on their favourable alleles to offspring. Frequency of unfavourable alleles decreases

Question 13

What is stabilising selection?

Answer 13

Occurs when environmental conditions stay the same. Individuals closest to the mean are favoured and any new characteristics are selected against. Results in low diversity

Question 14

What is directional selection?

Answer 14

Occurs when environmental conditions change. Individuals with phenotypes suited to the new conditions will survive and pass on their genes. Over time the mean of the population will move towards these characteristics

Question 15

What is disruptive selection?

Answer 15

The opposite to stabilising selection, both extremes of the normal distribution are favoured over the mean. Over time the population becomes phenotypically divided

Question 16

Define speciation

Answer 16

Where a population is split and isolated, there are different selective pressures on the two groups. If the genetic makeup changes to the extent the two groups can no longer interbreed they become separate species

Question 17

What is meant by allopatric speciation?

Answer 17

Speciation resulting from a physical barrier e.g river or mountain range. The environments occupied by the two groups are different and therefore different alleles are favoured

Question 18

What is meant by sympatric speciation?

Answer 18

Speciation resulting from a non physical barrier e.g a mutation that no longer allows two organisms to produce fertile offspring. Any changes in anatomy or behaviour may also prevent breeding

Question 19

Define genetic drift

Answer 19

A change in a populations allele frequencies that occur due to chance rather than selective pressures.

Question 20

Why does genetic drift affect small populations more than large ones?

Answer 20

The gene pool is smaller so there are less alleles available and any changes in frequency becomes pronounced very quickly