In summer squash, two genes (A and B) interact to form the colour of the fruit. Figure 1 shows a drawing of a summer squash.
Figure 1
Gene A controls whether the fruit has pigmentation or not. The dominant allele of this gene, A, results in no pigmentation, the squash are white, while the recessive allele, a, results in pigmented fruit. Gene B controls which pigmentation (yellow or green) the fruit has; the dominant allele, B, causes the fruit to have yellow pigmentation and the recessive allele, b, results in the fruit having green pigmentation.
Scientists performed 4000 crosses in which white squash, heterozygous for both genes, were crossed with yellow squash, heterozygous for gene B. They expected white, yellow and green squash in the offspring in a 4 : 3 : 1 phenotypic ratio.
Complete the genetic diagram to show how this ratio of phenotypes would be produced.
Parental phenotypes | White | Yellow |
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Parental genotypes | | |
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Gamete genotypes | | |
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Offspring genotypes | |
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Offspring phenotypes | |
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