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Unit 4 · Practice
Heredity and evolution · Year 10 Science · Science understanding
Topic hub: Overview · Previous: Natural selection and evidence
Try these after Units 1–3 — they mix cell division, inheritance and evolution ideas.
Your turn
Try without peeking, then reveal the answers.
Q1. One sentence: why does meiosis increase genetic variation in offspring compared with only mitosis?
Sample answer
Meiosis makes gametes with new combinations of alleles (assortment and crossing over) and half the chromosome number so fertilisation combines DNA from two different individuals.
Q2. In peas, purple (P) is dominant to white (p). Two heterozygous purple plants are crossed. What fraction of offspring are expected to be white?
Sample answer
Pp × Pp → 1/4 pp (white phenotype).
Q3. Explain in two sentences why “the giraffe stretched its neck” is not a scientific explanation of long necks in giraffes.
Sample answer
Acquired stretching is not inherited. Scientific explanations invoke heritable variation in neck length and differential survival/reproduction so longer-necked individuals leave more descendants over time (natural selection).
Q4. Link the ideas: why is heritable variation in a population necessary for natural selection to change trait frequencies over generations?
Sample answer
If there were no heritable differences, survival and reproduction could not systematically favour some variants over others — there would be nothing stable to accumulate across generations. Variation (from mutation, meiosis and sexual reproduction) supplies differences selection can act on.