Can you use a dihybrid cross to predict the genetics of corn?
Introduction:
Explain Mendel’s Law of Dominance and Law of Independent Assortment and how they create diversity in offspring.
Hypothesis:
The following are traits in corn. You will be looking at corn that display both of these traits and trying to figure out the genotypes
of the parents of your corn!
Dominant allele
Recessive allele
Trait
Color
Purple (Y)
Yellow (y)
Texture
Smooth (W)
Wrinkly (w)
You will be determining the parents of the corn. The parents of the corn could have been:
1) Both heterozygotes for the two traits. (Dihybrid Cross)
2) One parent heterozygous for the two traits, the other parent homozygous recessive for the two traits. (Test Cross)
You will make two hypotheses…the If is the genotype for the parents…
Then predict the fraction of the phenotypes for the offspring: (hint: There will be 4 phenotypes for this cross!)
Phenotype
Fraction and %
Because…show your dihybird cross (your work)!
Methods:
Document a systematic way to determine the actual fraction of phenotypes offspring in your corn. Then have one partner (or pair)
count each of the two corn your group was provided. Make sure that corn #1 and corn #2 are not mixed up. Think about how
many kernels you might want to count and how you will get an approximation of the total.
Data and Analysis:
Corn #1:
Phenotype
# Counted
Total
Trend: Which of the predicted models fits this data set?
Corn #2:
Phenotype
# Counted
Fraction of Offspring (or %)
n/a
Fraction of Offspring (or %)
Total
n/a
Trend: Which of the predicted models fits this data set?
Conclusion:
1. Discuss which results support each of your hypotheses. Explain in terms of probability.
2. Explain Mendel’s Law of Dominance and Law of Independent Assortment in terms of the corn.
3. If you crossed a homozygous purple & smooth corn with a homozygous yellow & wrinkly corn, what would all of the
offspring look like and what would their genotype be?
4. How come some people accepted their hypothesis even though their % were not exactly what they predicted?
5. Is it better to count 10 or 100 kernels? Explain. Why did we look at corn, rather than human genetic traits within our
own families?
BONUS: Read about the Chi-square test. Try the test on your data and see if you should have rejected your hypothesis.
The chi-square test allows on to reject a hypothesis, but not really to accept. It just tells us that the original hypothesis
was possible. http://waynesword.palomar.edu/lmexer4.htm