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Cambridge IGCSE Biology practice

What is the first step in performing a test cross to find an unknown genotype?

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Show answerMonohybrid inheritance revisionRevise the key idea

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Monohybrid inheritance

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What is the first step in performing a test cross to find an unknown genotype?.

  1. A.Cross the unknown organism with a homozygous dominant organism
  2. B.Cross the unknown organism with a homozygous recessive organism
  3. C.Cross two unknown organisms
  4. D.Cross the unknown organism with a heterozygous organism

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Paper 4 structured question: Monohybrid inheritance

Paper 4Theory (Extended)3 marks

Description

Test Cross Procedure

A plant shows a dominant trait, but its genotype is unknown. To find out, it is crossed with a plant that is homozygous recessive for the same trait. The offspring are then observed for their phenotypes.

  1. a

    Explain how this test cross can determine the unknown genotype of the plant showing the dominant trait.

    Aim for approximately 3 distinct marking points.

    [3]