GCSE Biology: Inheritance and Genetics

Genetics is the most calculation-like corner of GCSE Biology: given a cross, you should be able to derive the offspring probabilities every time. This quiz builds from the vocabulary to the crosses and the named disorders.

The molecular questions cover DNA as a double-helix polymer, the genome as an organism's complete genetic material, and why sequencing the human genome matters — including its use in identifying genetic disorders. Meiosis is tested against its exam-critical contrast with mitosis: four daughter cells, genetically different, with half the chromosome number, and fertilisation restoring the full count.

The terminology question forces precision on the word set the whole topic depends on — genotype, phenotype, homozygous, heterozygous — by asking which definitions are correct, with one deliberately wrong definition to catch. Then the crosses: a Bb × Bb cross yielding a 25% chance of the recessive phenotype, and a polydactyly cross (Dd × dd) yielding 50% — both requiring an actual Punnett square, not pattern-matching. The named disorders appear exactly as the specification lists them: polydactyly caused by a dominant allele, cystic fibrosis by a recessive one, with a carrier question testing that a symptomless carrier of a recessive disorder must be heterozygous.

Sex determination closes the set: XX and XY, with the key insight that the father's gamete determines the outcome. Every cross in the quiz uses concrete alleles and every explanation walks the Punnett logic step by step — the working that Higher tier questions require you to show.

• Describe DNA, genes and the genome and why genome sequencing matters
• Contrast meiosis with mitosis in products and chromosome number
• Use genetic vocabulary precisely: genotype, phenotype, homozygous, heterozygous
• Derive offspring probabilities from Punnett squares for dominant and recessive crosses
• Explain inheritance of polydactyly, cystic fibrosis and biological sex

Topic scope follows the inheritance, variation and evolution section of the Department for Education's GCSE combined science subject content: DNA and the genome, meiosis, genetic inheritance including Punnett squares, inherited disorders and sex determination.