Can anyone help me solve this problem?

Genetics as it applies to evolution, molecular biology, and medical aspects.

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Can anyone help me solve this problem?

Post by AllYourBase » Tue Jun 22, 2010 7:11 pm

I'm having a bit of trouble with this problem in class, anyone have any help?

In one part of his study, Mendel crossed plants that were true-breeding for seed shape, seed color and seed coat color (which correlates with flower color, either purple or white). In the P generation, he crossed true-breeding spherical/yellow/purple with true-breeding wrinkled/green/white plants. The F1 from this cross were all spherical/yellow/purple. Then, as always, he self-fertilized the F1 plants to obtain 639 viable F2 seeds. He then grew these 639 F2 plants and analyzed their phenotypes, but in this case the phenotypes he focused on were whether or not the plants were true breeding (homozygous) or hybrid (heterozygous). He reports his results as follows:

Genotype Observed
Homozygous for 3 traits 77
Homozygous for 2 traits 228
Homozygous for 1 trait 256
Homozygous for 0 traits 78
NOTE: In this table, traits that are not homozygous were heterozygous; for example, plants that were “Homozygous for 1 trait” were heterozygous for the other two

1. Calculate the expected results from this cross under Mendel’s 2 princi- ples. First, calculate the probability that a plant from an F1× F1 cross would be homozygous for all three traits assuming Mendel’s hypotheses are correct and use that to determine the expected number of the 639 offspring that would be homozy- gous for all 3 traits. Then use the same technique to calculate the number of F2 plants that are homozygous for 2 traits and heterozygous for 1, and so on for each of the 4 possible combinations.
2. Construct and complete a χ2 table for these data. 3. Calculate χ2. 4. Interpret χ2. The critical value is 7.851.

Thanks everyone!

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