3.5.1 Human Impact on evolution

Question 1

Define ‘mutation’.

Answer 1

Any change to the quantity or structure of an organism’s DNA.

Question 2

Define ‘allele’.

Answer 2

A different version of a gene.

Question 3

Describe the steps that occur from a mutation to an increase in allele frequency in a population.

Answer 3

• A mutation occurs within a population that results in a formation of a new allele.
• If the mutation occurs in a gamete, the allele is passed onto the offspring.
• The phenotype of the resulting offspring will be changed, adding to the phenotypic variation within the population.
• If the individuals that inherit the allele have a selective advantage, they are more likely to survive and reproduce than individuals without the allele.
• After several generations, the frequency of the allele will increase within the population.

Question 4

Define ‘intraspecific competition’.

Answer 4

Competition that occurs between members of the same species.

Question 5

Define ‘interspecific competition’.

Answer 5

Competition that occurs between members of different species.

Question 6

When does intraspecific competition occur within a population?

Answer 6

When large numbers of offspring are produced within the population, producing more offspring than the environment can support.

Question 7

Define ‘species’.

Answer 7

A group of similar organisms that can freely interbreed to produce fertile offspring.

Question 8

Define ‘speciation’.

Answer 8

The development of a new species from a previously existing species.

Question 9

Explain the two ways that a new species may arise.

Answer 9

• Individuals from two different species cross-fertilise and produce a fertile hybrid.
• Groups within the population become reproductively isolated.

Question 10

Name the two forms of speciation that occur through reproductive isolation.

Answer 10

• Allopatric speciation

- Sympatric speciation

Question 11

When does allopatric speciation occur?

Answer 11

When populations are prevented from interbreeding because they become geographically isolated.

Question 12

When does sympatric speciation occur?

Answer 12

When populations living together become reproductively isolated.

Question 13

Describe the steps to allopatric speciation.

Answer 13

• A species occupies a specific area. Individuals within the area form a single gene pool and freely interbreed.
• A physical barrier forms across the area, reducing it to two isolated regions. The distance between the two regions is too great for the two species to cross/there is no corridor habitat.
• Climatic changes occur in one region, resulting in much different conditions on either side of the barrier. Selection pressures in the two isolated regions are now different.
• The differing selection pressures in the two areas result in the gene pools of the two groups becoming very different. There is no gene flow between the groups.
• A removal of the barrier results in the two groups reuniting. The two groups are no longer capable of interbreeding to produce fertile offspring. They are now two separate species with their own gene pools.