Evolution may lead to speciation

Question 1

Genetic factors that cause phenotypic variation within a species

Answer 1

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

Question 2

Why does natural selection occur?

Answer 2

1. Predation
2. Disease
3. Competition

All result in differential survival and reproduction

Question 3

How does natural selection cause a change in a population’s gene pool over generations?

Answer 3

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

Question 4

What is Stabilising selection?

Answer 4

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

Question 5

What is Directional selection?

Answer 5

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

Question 6

What is Disruptive selection?

Answer 6

Opposite of stabilising selection, in that both extremes of normal distribution are favoured over mean. Over time, population becomes phenotypically divided.

Question 7

Define Speciation

Answer 7

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

Question 8

What is meant by Allopatric speciation?

Answer 8

Speciation resulting from physical barrier e.g. river, mountain range. Environments occupied by to groups are different, & so different alleles are favoured

Question 9

What is meant by Sympatric speciation?

Answer 9

Speciation resulting from non-physical barrier e.g. mutation that no longer allows 2 organisms to produce fertile offspring. Any changes in anatomy or behaviour may also prevent breeding

Question 10

Define Genetic Drift

Answer 10

Change in population’s alleles frequencies that occur due to chance rather than selective pressures. (caused by ‘sampling error’ during reproduction)

Question 11

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

Answer 11

Gene pool is smaller, so there are less alleles available & any change in frequency becomes pronounced very quickly