DNA & Genetics is a core part of IB Biology. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
DNAA double helix carrying the genetic code.
GeneA section of DNA coding for a protein.
AlleleA version of a gene.
Genotype & phenotypeGenetic makeup and the characteristics shown.
InheritanceDominant and recessive alleles; Punnett squares.
MutationA change in DNA that can alter a protein.
RibosomerRNA + protein, 70S/80S
A siteHolds incoming aminoacyl-tRNA
P siteHolds peptidyl-tRNA
E siteExit for deacylated tRNA
Peptidyl transferaseRibozyme forming peptide bond
RibozymeRNA acting as catalyst
PromoterRegion where RNA pol binds (e.g. TATA)
RNA polymerase IIEukaryotic mRNA transcribing enzyme
Common mistakes to avoid
Questions where students often pick the tempting wrong answer — make sure you know the right one:
Where is DNA found in a cell?✗ Only in the nucleus. ✓ Mainly in the nucleus, but also in mitochondria (and chloroplasts).
Does each gene control one characteristic on its own?✗ Yes, every trait is controlled by a single gene alone. ✓ No — many traits are polygenic and affected by the environment.
Will a recessive allele die out over generations?✗ Yes, recessive alleles are weak and disappear. ✓ No — it persists, carried by heterozygotes.
Practise DNA & Genetics — free games
Test yourself with these quick revision games for this topic:
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