Scholars from the Days of the Ancient Greeks to the End of the Last Century Believed That

Name: ______

Date: ______

Scholars from the days of the ancient Greeks to the end of the last century believed that traits of offspring were merely a blend of the parental traits, a sort of average. In 1958, Mendel tested this belief by placing pollen from a pure tall strain of peas on the stigma of a pure dwarf strain. Scientists of Mendel’s day would have predicted that the offspring of the cross would be intermediate in height, but they were actually all tall! From this and other observations, Mendel worked out his laws of heredity.

The Mendelian principles also apply to kernel color and shape in corn, traits which are easier to study. Each corn kernel represents a separate offspring of a cross between the female parent (of which the cob is a part) and the male parent (which supplied the pollen). The pollen fertilizes the ovules which develop into the kernels you will examine.

·  Monohybrid corn

·  calculator

1.  For this cross, the breeder selected a strain whose offspring always formed purple kernels and a second strain whose offspring always formed yellow kernels when self-pollinating. These two parent strains were mated (PP x pp) and the kernels of corn produced are the F1 generation (Pp). A second cross was then made by allowing F1 parents to self-pollinate (Pp x Pp). The offspring of this cross are the F2 generation. You will examine an F2 ear.

2.  Obtain an ear of corn.

3.  Determine number of purple kernels and yellow kernels.

a)  Count the total number of rows of kernels:______

b)  Divide by 2:______

c)  Choose 2 random rows and count the total number of purple kernels:______

d)  In the same 2 random rows, count the total number of yellow kernels:______

e)  Multiply 3b) x 3c):______This is the estimated total number of purple kernels in the entire ear of corn.

f)  Multiply 3b) x 3d):______This is the estimated total number of yellow kernels in the entire ear of corn.

4.  Determine the percent purple and percent yellow (i.e. # purple / (# purple + # yellow) x 100).

a)  % purple: ______b) % yellow: ______

5.  Record your data on your own data table.

6.  Copy the class data.

7.  Calculate the percent purple and percent yellow for the class results.

8.  Return the corn to the monohybrid tray & answer the lab wrap-up questions on a separate piece of paper.

Directions: Answer the following on a separate piece of paper.

Short Answer Questions:

1.  What percent ratio was obtained between purple and yellow kernels for your data?

2.  What percent ratio was obtained between purple and yellow kernels for the class data?

3.  Using the Punnett method (P = purple allele, p = yellow allele), show the parental cross between the pure purple and pure yellow plants. Calculate the expected genotypic ratio and phenotypic ratio for the offspring (F1).

4.  Using the Punnett square method, show the F1 x F1 cross. Calculate the expected genotypic ratio and phenotypic ration for the offspring (F2).

HONORS Discussion Questions:

5.  Perform a Chi-Square comparison of the actual to the expected data. Show your work!

6.  Explain why you might expect differences between your data and class data.

7.  Use you knowledge of Punnett squares to suggest an explanation of the possible differences between the expected and actual phenotypic ratios.

8.  Can you tell whether a purple kernel is pure or hybrid by looking at it? Explain.

Monohybrid Cross: Pp x Pp

Your Data:

Purple / Yellow / Total

Number

Percent

Class Data:

Initials

/ # Purple / # Yellow
Total
Percent