evolution may lead to speciation

Question 1

Give genetic factors that cause phenotypic variation within a species

Answer 1

• Mutation of alleles
• Random fertilisation by gametes
• Crossing over of chromatids and independant segregation of chromosomes during meiosis

Question 2

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

Answer 2

Environmental factors

Question 3

Define evolution

Answer 3

The change in frequency of an allele in a population over time

Question 4

Why does natural selection occur?

Answer 4

Due to selection pressures such as:
1. Predation
2. Disease
3. Competition

Question 5

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

Answer 5

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

Question 6

Describe stabilising selection

Answer 6

• Occurs when environmental conditions stay the same
• Individuals closest to the mean are favoured
• Any new characteristics are favoured against
• Results in low diversity

Question 7

Describe directional selection

Answer 7

• Occurs when environmental conditions change
• Individuals with a single extreme phenotype suited to the new conditions survive and - Over time the mean of the population moves towards these characteristics

Question 8

Describe disruptive selection

Answer 8

• Individuals with alleles for extreme phenotypes at either end are more likely to survive and reproduce
• Occurs when environment favours more than one phenotype

Question 9

Define speciation

Answer 9

It is the development of a new species from an existing species

Question 10

Explain speciation

Answer 10

• Where a population is split and isolated, there are different selective pressures on the 2 groups
• If the genetic makeup changes to the extent that the two groups can’t interbreed
• They have become separate species

Question 11

What is meant by allopatric speciation?

Answer 11

• Speciation resulting from a physical barrier
• The environments occupied by the 2 groups are different and therefore different alleles are favoured

Question 12

What is meant by sympatric speciation?

Answer 12

• Speciation resulting from a non-physical barrier
• Any changes in anatomy or behaviour may prevent breeding

Question 13

Why does reproductive isolation occur

Answer 13

Because changes in alleles and phenotypes in some individuals prevent them from breeding successfully with individuals without these changes

Question 14

What are some of the changes that can occur to cause reproductive isolation?

Answer 14

1. Seasonal - individuals from the same population develop different flowering/mating seasons
2. Mechanical - changes in genitalia prevent successful mating
3. Behavioural - a group of individuals develop courtship rituals that aren’t attractive to the main population

Question 15

Define genetic drift

Answer 15

A change in a population’s allele frequencies that occurs due to chance rather than selective pressures

Question 16

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

Answer 16

• The gene pool is smaller
• So fewer alleles are available
• Any change in frequency becomes expressed quickly