TOPIC 7 - evolution may lead to speciation

Question 1

give genetic factors that cause phenotypic variation within a species.

Answer 1

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

Question 2

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

Answer 2

environmental influences

Question 3

why does natural selection occur?

Answer 3

1. predation
2. disease
3. competition

all resulting in differential survival and reproduction.

Question 4

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

Answer 4

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

Question 5

define speciation?

Answer 5

the process of forming new species, which occurs when populations become reproductively isolated and have no gene flow between them. if genetic makeup changes between two groups they can no longer interbreed, and have become separate species

Question 6

what is meant by allopatric speciation?

Answer 6

reproductive isolation is due to geographical reasons = geographic isolation
eg. river, mountain range

• the environments occupied by the 2 groups are different, therefore diff alleles are favoured

Question 7

what is meant by sympatric speciation?

Answer 7

Speciation resulting from non-physical barrier
- morphological reason ( changes in anatomy )
- seasonal
- behavioural

these reasons can prevent breeding

Question 8

define genetic drift.

Answer 8

change in a populations allele frequency that occurs due to chance rather than selective pressures

Question 9

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

Answer 9

the gene pool is smaller = less alleles available
- any change in frequency becomes pronounced quickly

Question 10

what is stabilising selection?

Answer 10

• stable environment
• both extremes of phenotypes are less likely to reproduce
• mean phenotype is favoured remains the same
• results in low diversity

Question 11

what is directional selection?

Answer 11

• change to the environment
• individuals with the phenotypes suited to the new conditions will survive and pass on their genes
• overtime, mean phenotype moves towards these characteristics

Question 12

what is disruptive selection?

Answer 12

• opposite of stabilising selection
• both extremes of the phenotype are favoured over the mean
  -over time the population becomes phenotypically divided