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4
AB,Ab,aB,ab.
Class 9 · English Medium · Pearson Edexcel · Biology
Reproduction, inheritance and variation
Distinguish independent assortment from linked inheritance.
Original Kidemy further-topic investigation. This optional lesson is shared by related upper pathways; select suitable depth with a teacher. It does not certify complete grade or board coverage.
Learn the idea
A two-gene cross uses an independent-assortment model only when its assumptions apply. Genes close together on one chromosome can be linked, producing gamete frequencies unlike the simple independent model. Recombination can produce new combinations; observed counts need sampling uncertainty.
Worked example
Under independent assortment, an AaBb parent forms AB,Ab,aB,ab gametes equally. Under a linked model those four probabilities may differ. The notation alone does not prove independence.
- State the model.
- Check probabilities total 1.
- Explain both biological and sampling limits.
Your written practice
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1/4
Four equal types.
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1/4
Multiply under independence.
Write in your own words. A guardian or teacher should review this response.
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The allele positions and linkage affect which combinations are inherited together.
Explain the missing arrangement information.
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A finite sample varies by chance even under the model.
Describe expected proportions as repeated-sample patterns, not a fixed schedule.
Apply the idea
Compare independent and linked gamete tables using clearly fictional probabilities.
Review with a guardian or teacher
- Use the stated evidence or givens.
- Show reasoning rather than only a result.
- Review and explain one correction.
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