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2024Q5(v)(b)Genetics – Some Basic Fundamentals
Short answerModerate1 mark
5(v)

Given below is a schematic representation of the inheritance of the shape of seeds of garden pea. Answer the questions that follow.

Figure for this question

What does the ratio 3 : 1 in the F2 generation represent?

Topic: Monohybrid ratio

Previous-year question practice database

Answer

Exam answer

It is the PHENOTYPIC RATIO of the F2 generation of a MONOHYBRID cross — three plants showing the dominant character (round seeds) to every one showing the recessive character (wrinkled seeds).

Explanation

Say PHENOTYPIC, because the genotypic ratio of the same cross is different: 1 RR : 2 Rr : 1 rr. Three of those four LOOK round (RR, Rr, Rr) and one looks wrinkled (rr), which is where 3:1 comes from.

So one cross gives two different ratios: PHENOTYPIC (what they look like) — 3 : 1 GENOTYPIC (what alleles they carry) — 1 : 2 : 1 Read which one the question wants.

Compare the DIHYBRID ratio 9:3:3:1, which applies when two characters are followed together — as in the 2025 paper.

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