Homework3Solution - What is a likely explanation for these...

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Biology 214/414 Homework #3 Due Friday, 9-11-09 (in class) Solution The geraniums in my Mother’s garden have flowers of three colors, white, red and pink, but surprisingly the colors are not due to incomplete dominance at a single gene (and so are not inherited like flower color in snapdragons). Instead, flower color in the geraniums is due to the action of two different genes, each with two alleles, which, in both cases exhibit simple dominance/recessiveness. Red geraniums that are homozygous for both genes are crossed with white geraniums, also homozygous for both genes. The resulting F1 plants are all red, but when the F1’s are crossed with each other, red, pink, and white flowered plants are obtained in the ratio of 9:6:1.
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Unformatted text preview: What is a likely explanation for these results? The following scenario works: The parents are: homozygous red flowered plants: AABB homozygous white flowered plants: aabb with A dominant over a and B dominant over b red X white parents gives F1’s, which are all AaBb The F1 X F1 cross is then AaBb X AaBb, which gives offspring in the ratio of 9 A-B-:3 A-bb:3 aaB-:1 aabb (remember that A-B- is a shorthand and includes all of AABB, AaBB, AABb and AaBb, and so forth for the A-bb and aaB- classes). It appears that having the dominant phenotype for both genes gives red flowers, having the recessive phenotype for both genes gives white flowers and having either gene dominant with the other recessive gives pink flowers....
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