Paper 2 - Speciation

Question 1

Allopatric Speciation

Answer 1

Original population becomes geographically isolated - there is no gene flow between the 2 populations.

Random mutations occur in each separate population leading to variation.

Each population experiences different selection / environmental pressures.

Different alleles will be advantageous in the different populations and will be selected for.

Those with advantageous alleles are more likely to survive, reproduce and pass on the advantageous allele to their offspring.

Allele frequencies change in the different populations.

Eventually, the gene pools of the 2 populations is so different that they can no longer interbreed to give fertile offspring – they are 2 separate species.

Question 2

Sympatric Speciation

Answer 2

Occurs in the same population – random mutations cause reproductive isolation of some members of population – no gene flow.

Different alleles will be selected for and passed on.

Allele frequencies change.

Results in disruptive selection.

Eventually, the gene pools are so different that they can no longer interbreed to give fertile offspring – they are 2 separate species.

Question 3

How would a change in a protein lead to speciation ?

Answer 3

If the receptor had a different tertiary structure, it would not be recognised by the other gamete, and they would not successfully fuse.
If another organism in the population produced a gamete that could recognise this receptor (due to a complimentary mutation), they would be able to fuse and produce an offspring – the 2 organisms would be reproductively isolated from the rest.

Question 4

Define evolution

Answer 4

A change in the allele frequencies in a population over time