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SingaporeCombined ScienceQuick questions

Biology: Genetics and Ecology

Quick questions on Inheritance and monohybrid genetics explained: O-Level Combined Science

4short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What is a worked cross pattern?
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Crossing two heterozygous tall plants (Tt with Tt) gives offspring TT, Tt, Tt, tt, a ratio of 3 tall : 1 short. Crossing heterozygous with homozygous recessive (Tt with tt) gives Tt, tt, Tt, tt, a ratio of 1 tall : 1 short. The diagram gives the ratio every time.
What is q1?
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Define the terms dominant allele and recessive allele. [2 marks]
What is q2?
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A plant has the genotype Tt for height, where T (tall) is dominant. State its phenotype and the gametes it can make. [2 marks]
What is q3?
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Two heterozygous plants (Tt) are crossed. State the expected ratio of tall to short offspring. [2 marks]

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