IB Biology: What Causes Genetic Variation in Populations?

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Mutations can occur because of DNA replication errors or because of mutagens (like UV or certain chemicals). They can be neutral, harmful, or beneficial; what matters for populations is that beneficial mutations can increase in frequency over generations.

If you want syllabus-aligned wording, revise mutation as a source of variation using D1.3 Mutations and Gene Editing and the D1.3.7 Mutation as a source of genetic variation Notes.

Meiosis: shuffling alleles before fertilization

In IB Biology, meiosis creates variation even if no new mutations occur. It does this by making gametes genetically different.

Crossing over (recombination) in prophase I

Homologous chromosomes pair up and exchange segments between non-sister chromatids. This creates new combinations of alleles on the same chromosome (recombinant chromatids). For a clear explanation with the right terminology, see How genetic recombination during meiosis contributes to diversity.

Independent assortment in metaphase I

Homologous pairs line up randomly at the equator. This means maternal and paternal chromosomes are separated into gametes in unpredictable combinations. Revision support: How random orientation during metaphase I increases genetic variation and the background stages in 1.6 Cell division Notes.

Sexual reproduction: randomness multiplied

Sexual reproduction increases genetic variation because fertilization combines one random gamete with another random gamete. Even if two parents are the same, the specific pairing of gametes produces a unique genotype in offspring.

This is why siblings are not genetic copies (identical twins aside), and why populations contain enough diversity for selection pressures to act.

Why genetic variation matters (and how it’s tested)

In IB Biology, genetic variation is rarely a standalone fact. It’s usually the first step in a chain: variation --> selection pressure --> differential survival/reproduction --> allele frequency change.

Expect data-based questions where you interpret allele frequency shifts, explain why low variation can increase extinction risk, or connect meiosis processes to observed phenotypic diversity. To tighten definitions like gene, allele, and locus, review 3.1 Genes Notes and reinforce inheritance language in IB Biology Topic D3.2 Inheritance.

Final takeaway for IB Biology students

Genetic variation isn’t “extra detail” in IB Biology. It’s the opening chapter of nearly every evolution story you’ll be asked to explain: mutation introduces new alleles, meiosis reshuffles them, and sexual reproduction mixes them again. If you can state those causes cleanly and link them to allele frequency change, you’re already writing in examiner-friendly language.

To lock it in, use RevisionDojo as your revision spine: practise with the Genetics Questionbank, revisit core concepts in D1.3 Mutations and Gene Editing, and tighten definitions with 3.1 Genes Notes.