Biology 22 Corn Genetics

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Biology 22 Corn Genetics

For this exercise, you will investigate inheritance of kernel color in the corn Zeamays. Epistatic interactions will be demonstrated by the outcome of three genetic crosses, designated C, D and F. In each case, parental corn has been bred to obtain an F1 generation. F1 individuals are crossed to each other to produce an F2 generation. You will analyze kernel color for F2 ears of corn.

For an ear of corn, each kernel represents a separate outcome from the cross between the parents. Each kernel therefore has its own genotype and phenotype. Two elements that contribute to kernel color include the aleurone layer and the endosperm. The aleurone layer is located just inside the outer pericarp layer. The endosperm, a source of nutrition for the developing seedling, is located below the aleurone layer. Endosperm color can be masked by aleurone color since the aleurone layer covers the endosperm.

Several genes are involved in determining kernel color and the effects of their alleles are outlined in the table below.

Trait / Genotype / Phenotypic Effect / Relationship
Endosperm Color / Y_ / Yellow Endosperm / Y > y
yy / White endosperm
Aleurone Color / R_ / Purple Aleurone / R > r
rr / Colorless aleurone
Aleurone Color Inhibitor / C’_ / No aleurone color in the presence of color alleles like R / C’ > C > c
CC or Cc / Aleurone Color in the presence of color alleles like R
cc / Colorless aleurone layer in the presence of color genes like R
Aleurone Color Modifier / P_ / No effect on aleurone layer / P > p
pp / Changes purple aleurone to red aleurone in the presence of R_

For your analysis:

1. Obtain an F2 ear of corn and use adhesive dots to mark the boundaries of a section containing 10 rows. A row is oriented from tip to tip of the ear, in the longer direction. Be careful not to tear the cellophane covering the ear.
2. Record the number of kernels of each color that are found within the boundaries. Record your data directly on the accompanying worksheet pages.
3. Predict the expected genetic ratio for each set of data and use a chi-square test to determine if your data fits the expected ratio.

Biology 22: Corn Genetics Worksheet NAME______

Cross C

Parental Phenotypes / Yellow X Yellow
Parental Genotypes /

YYC’C’RR X YYCCrr

F1 Phenotype /

Yellow

F1 x F1 Genotypes / YYC’CRr X YYC’CRr
F2 Phenotypes / Yellow / Purple
Class Totals for Observed Numbers of Kernels in F2 generation

In the space below, illustrate the expected genotypes for the F1 x F1 cross with a Punnett Square. What is the expected phenotypic ratio for Cross C in the F2 generation?

Use a chi-square analysis to test the expected ratio for the F2 of Cross C.

Phenotype / Observed
Number / Expected
Ratio / Expected
Number / (O-E) / (O-E)2 / (O-E)2/E

Total =

Chi-square ______

Number of degrees of freedom=

Probability of a match=

On the basis of your chi-square test, does your data support the expected ratio? If so, indicate the criterion you used to justify the support. If not, give a plausible reason for the failure of the data to reflect the predicted ratio.

Biology 22: Corn Genetics Worksheet NAME______

Cross D

Parental Phenotypes / Purple X White
Parental Genotypes /

yyPPRR X yypprr

F1 Phenotype /

Purple

F1 x F1 Genotypes / yyPpRr X yyPpRr
F2 Phenotypes / Purple / Red / White
Class Totals for Observed Numbers of Kernels in F2 generation

In the space below, illustrate the expected genotypes for the F1 x F1 cross with a Punnett Square. What is the expected phenotypic ratio for Cross D in the F2 generation?

Use a chi-square analysis to test the expected ratio for the F2 of Cross D.

Phenotype / Observed
Number / Expected
Ratio / Expected
Number / (O-E) / (O-E)2 / (O-E)2/E

Total =

Chi-square ______

Number of degrees of freedom=

Probability of a match=

On the basis of your chi-square test, does your data support the expected ratio? If so, indicate the criterion you used to justify the support. If not, give a plausible reason for the failure of the data to reflect the predicted ratio.

Biology 22: Corn Genetics Worksheet NAME______

Cross F

Parental Phenotypes / White X White
Parental Genotypes /

yyCCrr X yyccRR

F1 Phenotype /

Purple

F1 x F1 Genotypes / yyCcRr X yyCcRr
F2 Phenotypes / Purple / White
Class Totals for Observed Numbers of Kernels in F2 generation

In the space below, illustrate the expected genotypes for the F1 x F1 cross with a Punnett Square. What is the expected phenotypic ratio for Cross E in the F2 generation?

Use a chi-square analysis to test the expected ratio for the F2 of Cross F.

Phenotype / Observed
Number / Expected
Ratio / Expected
Number / (O-E) / (O-E)2 / (O-E)2/E

Total =

Chi-square ______

Number of degrees of freedom=

Probability of a match=

On the basis of your chi-square test, does your data support the expected ratio? If so, indicate the criterion you used to justify the support. If not, give a plausible reason for the failure of the data to reflect the predicted ratio.