Lab 26 Corn Two Trait Genetics
Introduction
Gregor Mendel is called the father of genetics because he analyze his results mathematically.
From this data he determined two principles: the Principle of Segregation (which you learned
with Wisconsin Fast plants) and the Principle of Independent Assortment. The Principle of
Independent Assortment states due to crossing over during meiosis, alleles of a trait will separate
into gametes independently of the other traits allowing for all variations to be present.
Parent Generation
F1 generation
F2 generation
In this investigation you will count kernels in an ear of corn. A complete ear represents a
compact population of offspring which may be counted to show Mendel’s principle. Mature
corn plants produce ears that contain hundreds of seeds or kernels. Each seed is formed
through fertilization of a different egg and sperm. Therefore, each kernel on an ear of corn
can grow into a whole new plant.
Some grains are purple and others are yellow. The purple color is produced by a pigmented
within the grains. If the pigment is not present then the corn is yellow. Sweet corn grains can
be recognized because they wrinkle upon drying while starchy grains remain smooth. An
individual grain may be purple and starchy, purple and sweet, yellow and starchy, or yellow
and sweet. Answer the questions in the prelab.
For extra credit, read about why corn can be speckled on these websites and explain it on the
prelab. DNA from the Beginning | Nobel Prize
first page
email us
glossary
references
26. 1
Lab 26 Corn Two Trait Genetics
Procedure
Take a look at the pictures on the previous page. Can you tell if purple or yellow is dominant?
How do you know?
(hover your mouse over the question mark for the answer)
If you cross a homozygous starchy with a homozygous sweet corn plant, then all the offspring
will be starchy. Is starchy or sweet dominant?
How do you know?
The ear of corn below shows what you should expect to see during this lab. Count the number
of each color and determine if it follows Mendel’s Principle of Independent Assortment by
completing a chi square calculation. Hover over the question marks to see how many kernels
counted,
the expected numbers
and the chi-square critical value.
Does the data
follow the hypothesis?
How do you know?
yellow wrinkled
purple smooth
purple wrinkled
yellow smooth
first page
email us
glossary
references
26. 2
Lab 26 Corn Two Trait Genetics
Obtain an F2 generation ear of corn. One person should call out the phenotypes while the
other tallies them in Table 1 on the answer sheet. Then switch to make sure that each of you
know how to determine the phenotypes. Please be careful with the corn cobs as they are
fragile; do not remove any of the kernels as you count.
Count and record the number of kernels of each phenotype. An individual
grain may be purple and starchy, purple and sweet, yellow and starchy, or
yellow and sweet. If the kernel is speckled do not count the kernel.
Collect the class data. You will use this website to determine if there is a statistical difference
between the observed and expected values. Enter the names of the categories into the first
column: red and green. Enter the number of plants counted (observed data) in the second
column. Then enter the expected data in the third column. Press the calculate now button.
The next screen will tell you the Chi-Square test statistic and the Degrees of Freedom that
you will use to look up the Critical value. It also mentions whether or not the difference
between the observed and expected is statistically significant. If the difference is not statistically
significant then we have no evidence against Mendel’s Principle of Segregation; therefore our
data follows our hypothesis. Be sure to record this information on your answer sheet and
answer the questions.
Don’t forget to complete your homework.
first page
email us
glossary
references
26. 3
Lab 26 Corn Two Trait Genetics
References
Corn Dihybrid Genetics. Carolina Biological Supply. Burlington, NC.
Holsinger, Rachel and Debbie Wheeler. Lab 26: Corn Two Trait Genetics. Sayre School:
Lexington, KY. April 5, 2015.
Muskopf, Shannan. Corn Genetics and Chi Square Analysis. 2001. The Biology Corner.
April 22, 2007. http://www.biologycorner.com/
first page
email us
glossary
references
26. 4