Fig. 5.1 shows a cob with yellow and white seeds, obtained from a maize plant. The maize cob has 13 yellow seeds and 39 white seeds.

1. aWhat is the genetic ratio shown by these seeds? [1]
2. bSuggest which of the two colours, yellow or white, is controlled by a dominant allele. [1]
3. cExplain, with a full genetic diagram, how the ratio was achieved. Use symbol R for the dominant allele and r for the recessive allele. [5]

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