Name____________
_________________
Hr_______
PATTERNS OF HERDITY
Inheritance of Patterns through one and two characteristics
General Objectives:
1. To observe evidence for the chromosome theory of heredity in humans, other
animals and plants.
2. To relate the chromosome theory of heredity to current practices in genetic
counseling
3. To practice, learn and utilize genotypic and phenotypic terminology and ratios.
Procedure:
Each student will obtain an ear of corn. One student may then classify the kernels while
the other acts as a recorder. You will not be told whether or not it is a monohybrid cross
or a backcross ear or a dihybrid cross ear. This is something you will need to do through
careful observations! BE CAREFUL when handling the ears of corn so that the kernels
will not become loose and drop out. Also, DO NOT PICK the kernels from the ears, for
they will need to used by other classes.
Instructions:
1. READ THE ENTIRE INSTRUCTIONS.
2. Complete the punnet squares and the expected ratios on page two and three.
3. Observe your ear of corn and determine the type you have.
4. Count the kernels and record the number of kernels of each trait in the appropriate
data tables on pages 3 and 4. The student counting can use a piece of masking tape to be
used as a starting point by marking on the tape the starting row. Then (s)he should call
off the characteristics of each kernel in each row until (s)he returns to the mark on the
tape. As the characteristics are called out, the student who does the tallying should
record the data in its’ proper place in the data table.
5. Select a different cob of corn that fits the description of one of the other categories.
There are a total of three categories- monohybrid cross, one trait test cross, and dihybrid
cross.
MONOHYBRID CROSS
P1 = PP x pp
P=Purple (dominant)
p=yellow (recessive)
F1= the offspring of the above cross which will result in 100% Pp (genotype), purple
(phenotype)
F2= offspring of F1-------Fill out punnet square below to get expected ratios
Expected Ratio from Punnet Square_____:_______
TEST CROSS
P1= PP x pp
F1= Pp
Cross an F1 offspring (Pp) with a pure recessive on the punnet square below.
Expected Ratio_______;______
DIHYBRID CROSS
P1= PPSS x ppss
S=smooth (dominant) s=wrinkled (recessive)
F1= PpSs the offspring will be all purple smooth (phenotype)
Take the F1 and cross it to get F2 expected ratios. Fill out the punnet square below.
PpSs x PpSs
Expected phenotypic ratio_____:_____:______:_______
DATA TABLES
Monohybrid data table
Testcross data table
Purple
Purple
Yellow
Total kernels
%
Expected %=_______:_______
Yellow
Total kernels
%
%
Expected %=_____:______
%
Dihybrid data table
Purple smooth
P_S_
Dom-dom
Purple wrinkled
P_ss
Dom-rec
Yellow smooth
ppS__
rec-dom
Yellow wrinkled
Ppss
Rec-rec
Total kernels
%
%
%
%
Expected ratios (out of 100, get #s from coin lab)_______:_______:_______:________
Conclusion Questions:
1. What is the determining factor into deciding whether or not the traits are dominant or
recessive? Does this mean that this is the way it always is in nature???? Explain your
answer.
2. List the phenotypes of kernels in the two trait corn.
3.What is the most common?
4. What is the least common?
5. If you were a farmer and wanted your clients to have to rely on you for plants instead
of them harvesting their own seeds from the plants they get from you what type of plants
would you want to sell? (give the genotype) and explain why.