Notes for A3.1.10 Comparison of genome sizes - IB | RevisionDojo
A3.1.10 Comparison of genome sizes Notes
Written by official IB examiners
Genome Size and Complexity
Larger genomes do not necessarily indicate greater biological complexity.
Key contributors to variation include:
Non-coding DNA: repetitive sequences, introns, and transposable elements.
Polyploidy: whole-genome duplication, especially common in plants.
Gene duplication and intron variation: expansion of non-essential DNA regions.
Example
Humans (~3.2 × 10⁹ bp) have a smaller genome than some amphibians or plants (>10¹¹ bp) despite higher organismal complexity.
Summary Table (Typical Genome Sizes)
Group
Approximate Genome Size
Notable Feature
Bacteria
1–10 Mbp
Compact, mostly coding DNA
Fungi
10–100 Mbp
Moderate non-coding regions
Plants
100 Mbp – 100 Gbp
Polyploidy, high non-coding DNA
Animals
100 Mbp – 10 Gbp
Large variation; no link to complexity
Self review
Why might genome size increase without added complexity?
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DefinitionGenome sizeThe total amount of DNA in one haploid set of chromosomes of an organism, usually measured in base pairs (bp).
Genome sizes vary massively across life, from viruses to plants and animals. A key idea in biology is that a larger genome does not necessarily mean a more complex organism.
Analogy
A genome is like a book. A longer book is not automatically a better or more complicated story if lots of pages are blank, repeated, or copied twice.
Note
Genome size is often discussed with the "C-value" (amount of DNA per haploid genome). The surprising patterns are sometimes called the C-value paradox.
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