← Year 10 Biology

Year 10 Biology: recap

Answer each question in your head or on paper first, then check it.

Genetics

1. Where are the instructions?

Try firstWhat's the difference between a gene and an allele?

Check your answer

A gene is a section of DNA coding for a protein; an allele is one version of that gene.

DNA carries the instructions; a chromosome is one long coiled DNA molecule; a gene is a section of DNA coding for a protein; alleles are versions of a gene. Chromosomes come in pairs, one from each parent.

From body to gene · Sound on for the voiceover
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2. Why is every sperm and egg different?

Try firstWhy does meiosis make every gamete different?

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Each gamete gets one chromosome from each pair, and which one is random, so the combination differs.

Meiosis makes gametes with half the chromosomes: one from each pair, chosen at random, so almost every gamete is a different combination (over 8 million possible in humans). Mitosis makes identical cells for growth and repair.

Meiosis · Sound on for the voiceover
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3. Can you predict the offspring?

Try firstComplete Bb × Bb. What fraction of offspring are expected to show the recessive trait?

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BB, Bb, Bb, bb: 1 in 4 (25%).

Punnett square: each parent's possible gametes along the edges, every combination in the grid. It gives probabilities: Pp × Pp gives 1 PP : 2 Pp : 1 pp, so 3 dominant : 1 recessive phenotype. Genotype is the alleles; phenotype is the characteristic seen.

A Punnett square · Sound on for the voiceover
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Evolution

4. How different are individuals?

Try firstGive an example of inherited variation and one of environmental variation in humans.

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For example: blood group (inherited); a scar or a language spoken (environmental).

Variation: individuals in a population differ. Continuous (any value, such as height) or discontinuous (groups, such as blood group); inherited, environmental, or both. Only inherited variation is passed on, so only it drives evolution.

No two beetles quite the same colour: continuous variation in one population.
No two beetles quite the same colour: continuous variation in one population.
Variation · Sound on for the voiceover
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5. Why did the beetles change?

Try firstExplain why the beetle population got paler on pale ground.

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Beetles varied in colour; birds ate the darker, more visible ones; paler beetles survived and bred, passing on their colour; over generations, the average colour got paler.

Natural selection: individuals vary; those best suited to the environment are more likely to survive and reproduce, passing on their alleles; over generations the population changes. Individuals don't change: the population does. "Fittest" depends on the environment.

Over millions of years this branches into a tree of life: all living things share ancestors, and DNA shows how closely they are related.

A population of beetles: each one a slightly different colour, on pale ground.
A population of beetles: each one a slightly different colour, on pale ground.
Natural selection · Sound on for the voiceover
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