In Mendels experiments with pea plants, one of the keys to his success was his a

Question

In Mendels experiments with pea plants, one of the keys to his success was his ability to take experimental data showing the number of individuals in each phenotypic class, and to transform it into a meaningful ratio (ie a ratio of containing only integers, or whole numbers) For the following dihybrid or trihybrid data sets, each number separated by a comma indicates the number of individuals in different phenotypic classes. For each example, indicate the most likely ratio underlying the experimental numbers and indicate the genotypes of the parents ( you can usa A/a, B/b, C/c etc to signify different genes and their alleles.)

a. 1817,611,599,202

b. 417,398,401,433

c. 127,117,125,135,130,132,114,133

Explanation / Answer

a)

1817,611,599,202

These numbers indicate the ratio: 9: 3: 3: 1. It is a phenotypic ratio of a dihybrid cross. For example, a cross between the AaBb × AaBb gives this phenotype. Here, parental genotype AA (round seed), bb (green seed), aa (wrinkled) and BB (yellow seed). Upon selfing between AA bb × aa BB gives AaBb (round and yellow) seeds in F1 generation. The selfing between AaBb × AaBb gives above phenotypic ratio.

b)

417,398,401,433

These numbers indicate the ratio: 1: 1: 1: 1. It is a dihybrid genotypic ratio of a testcross. For example, a cross between the AaBb × aabb gives this phenotype. The test cross will yield four progeny categories whose phenotypes will determine by the dominant or recessive allele contributed by the F1 hybrid. Here, the F1 traits are crossed with complete a recessive trait, which means one of their parents.

c)

127,117,125,135,130,132,114,133

These numbers indicate the ratio: 1: 1: 1: 1: 1: 1: 1: 1. It is a trihybrid genotypic ratio of a testcross.

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