Mutation increases genetic diversity by creating new alleles, while sexual reproduction increases diversity by combining existing alleles into new genotypes. This is HL-only content from IB ESS subtopic 3.1, Biodiversity and evolution.
The Reasoning and Mechanism
A mutation is a random change in an organism's DNA sequence. If it occurs in a cell that produces gametes and is inherited, it may introduce a new allele, which is an alternative form of a gene, into the population's gene pool.
Most mutations are neutral, some are harmful, and a small number may provide an advantage under particular environmental conditions. Mutation is therefore the original source of new genetic variation on which natural selection can act.
Sexual reproduction does not normally create new alleles. Instead, it creates new combinations of alleles through processes associated with meiosis and fertilization. These produce genetically different offspring, even when the offspring have the same parents.
| Mechanism | Effect on genetic diversity |
|---|---|
| Mutation | Creates new alleles through changes in DNA |
| Crossing over during meiosis | Exchanges DNA between homologous chromosomes, producing new allele combinations |
| Independent assortment | Distributes maternal and paternal chromosomes randomly among gametes |
| Random fertilization | Combines genetically different gametes unpredictably |
The common misconception is that sexual reproduction creates new alleles. It mainly reshuffles existing alleles; mutation creates genuinely new ones.
Greater genetic diversity can increase a population's resilience because some individuals may possess alleles that help them survive disease or environmental change. For example, genetically uniform Cavendish banana crops are highly vulnerable to Panama disease Tropical Race 4, showing how low diversity can threaten ecosystems, livelihoods, and food security.
Exam Technique
For an IB ESS explain question, state the mechanism and connect it to the outcome: mutation creates new alleles, sexual reproduction produces new allele combinations, and both increase variation within a population. Link this variation to natural selection, adaptation, and ecosystem resilience rather than simply stating that offspring are “different.”
