Coat color in corn kernels exhibits the complete dominance model, resulting in either purple or yellow kernels.
1. What additional phenotype might we expect if coat color exhibited a model of co-dominance?
2. What additional phenotype might we expect if coat color exhibited a model of incomplete dominance?
3. If you are given the phenotype of an F2 kernel (purple/smooth, purple/wrinkled, yellow/smooth, or yellow/wrinkled), can you know the genotype of that kernel? If so, which ones can be determined, and which can't? Explain.
4. Examine the actual phenotypic ratio from Exercise 3B and compare it to the predicted phenotypic ratio. Do the predicted and actual ratios match exactly? Provide a possible explanation for why the actual ratio didn't match the predicted ratio exactly.
Exercise 3B - In a dihybrid cross, we are following the patterns of inheritance of two different traits (genes). In the following exercise, you will determine how the previous traits, coat color and coat texture, combine in the offspring. To the uninformed, it might seem like the dominants should always travel together, so that when you have purple seeds, you will also have smooth seeds. This isn't necessarily the case, however. As long as the two genes reside on different chromosomes (i.e., are not linked), they should assort (combine) independently of one another in the offspring (Mendel's second law). We will test this assumption.
5. Which of Mendel's laws are you exploiting in the analysis of a dihybrid cross? Explain.
6. Are dominant characteristics always more frequent in a population than recessive characteristics?
7. Two heterozygous parents mate. What is the chance of them having an offspring that is homozygous recessive?
8. You meet someone with a straight little finger. Can you determine their genotype? Why or why not?