Explain how a new species can arise from an original population of organisms through the process of speciation.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A population of birds lives on a large mainland. Over thousands of years, some birds become isolated on a remote island with a different environment. Eventually, the island birds and mainland birds can no longer interbreed successfully.
Model answer (5 marks)
Genetic variation exists in the original population due to mutations and sexual reproduction.
The birds become geographically isolated, preventing interbreeding.
Different selection pressures act on each group, favouring different alleles.
Over many generations allele frequencies change, making the two populations increasingly genetically distinct.
Eventually the genetic differences are so great that interbreeding produces infertile offspring, so the groups are classified as separate species.
The birds become geographically isolated, preventing interbreeding.
Different selection pressures act on each group, favouring different alleles.
Over many generations allele frequencies change, making the two populations increasingly genetically distinct.
Eventually the genetic differences are so great that interbreeding produces infertile offspring, so the groups are classified as separate species.
Examiner tips
- Use the exact sequence of points from the mark scheme
- Show the causal link between isolation, selection and genetic change
- Mention ‘fertile offspring’ to demonstrate speciation criterion
Common mistakes
- Confusing isolation with lack of genetic variation
- Failing to state that infertile offspring indicates speciation
- Using vague terms like ‘different environments’ without linking to selection
Mark scheme (5 marks)
- Genetic variation exists within the original population due to mutations and/or sexual reproduction
- The two populations become geographically isolated, so they cannot interbreed
- Different selection pressures act on each population, so different alleles are advantageous in each environment
- Over many generations, the allele frequencies in each population change, so the two populations become increasingly different genetically
- The populations become so genetically different that they can no longer interbreed to produce fertile offspring, and are therefore classified as separate species
Key terms in this question
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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