Genetic Inheritance
Exercise 1: F1 Hybrid Cross
Results:
Punnett Square for F1 Cross ¡V Expected Genetic Outcomes
F1 Parent, genes: _________
(student to fill in the blanks)
¡ð alleles >
¡ñ alleles v
F1 Parent, genes:__________
(student fill in blank)
1. Expected phenotypic ratio of green to white progeny: _____:_____.
Calculation of Expected Ratio (Frequency) = __________ = Total Number of (Color) Seedlings ¡Ò Total of All Seedlings.
2. If 320 F2 offspring resulted from this F1 cross, how many would be green? White?
Table 1: Results of F1 Cross
Observed Phenotypes of F2 Progeny
# green plants = V # white plants = V Total # plants
Petri Dish 1 >
Petri Dish 2 >
Total
Observed Frequency of F2 Phenotype, Green:White = ______:______
Calculation of Observed Ratio (Frequency) = Total Number of (Color) Seedlings for Both Dishes ¡Ò Total of All Seedlings
Discussion:
A. Did the results support or refute the hypothesis? Explain.
B. How similar are the observed to the expected results from the Punnett Square?
C. If the results are not similar, how might the difference be explained?
D. Will a monohybrid F1 cross in corn yield the same ratio of expected phenotype in progeny as for the tobacco seedlings? Why or why not?
E. If available, compare your F2 seedling data to those of your classmates. Are the outcome ratios the same? Why might using a larger number of seedlings to determine this outcome be wise?
Exercise 2: Dihybrid Genetic Crosses
PROCEDURES:
1. Based on what you can conclude about its genetic makeup when told that the corn plant parent cross (P) pictured in Figure 2 is between a completely dominant plant and a completely recessive plant,
A. Construct and record a hypothesis about what the genetic makeup and the frequencies of the alleles for the F1 progeny plants in the dihybrid cross of corn will be. Record your hypothesis here:
B. If these F1 progeny are mated, what will be the resulting allelic frequency for the F2 progeny? Record this hypothesis here:
2. Based on the phenotype and genotype information for the P cross from 1 above, record the genotypes and Expected Frequencies for P and F1 in Table 9.2. Hint: One of the cobs contains all ppss kernels. Which one? Record the answer here:
3. Construct a Punnett Square for the P cross producing the F1 progeny. What is the only possible genetic outcome for the F1 progeny? What is the phenotypic outcome? Place your Punnett Square here:
4. Using the Punnett Square for F1 Dihybrid Cross, Figure 3, indicate the possible genetic outcomes for the F2 progeny here:
Results:
A. What are the two hypotheses that you made about the allelic frequencies of progeny produced by the crosses:
P x P?
F1 x F1?
B. Based on what you know about phenotypes and Figure 2, for the P generation, what is the corn plant genotype on each cob containing the P corn kernels.
One is completely dominant, so its genotype is ______________.
One is completely recessive, so its genotype is_____________.
C. Would it make a difference in the outcome of this cross if the genotype of one parent is PPss and the other is ppSS?
D. From the phenotype of the kernels on each P generation cob what would the predicted genotype of any F1 plant be?.
E. Given the 2n equation predict how many different genetic outcomes will be possible from an F1 cross resulting in the F2 generation in a dihybrid corn cross.
F. If a F2 corn cob resulting from this F1 cross contained 563 seeds, how many of the seeds would you expect to look like the F1 parent?
Table 2: Dihybrid Cross in Corn ¡V Results of P Cross
P = purple, p = yellow
S = smooth, s = wrinkled
(student to fill in all blanks _______ )
Generation Expected Alleles V Expected Alleles V
P >
dominant x recessive ______
_ppss_
F1 Progeny > _______
Frequency > _______
Figure 3: Punnett Square for F1 Dihybrid Cross
Expected Genotypic Outcomes
(student to fill in)
Parent 1 F1 ¡V can produce these gametes: ________V
(student to fill in)
¡ð
¡ñ
Parent 2 F1 ¡V can produce these gametes:
________>
Shaded portion above represents the F2 progeny genotype and phenotype. Student to fill in.
Table 3: Dihybrid Cross in Corn ¡V Results of F1 Cross in F2 Progeny
Phenotype of Progeny
(What they look like ¡V word description)
V Genetic Designations possible for this Phenotype
e.g., PPSS
V Predicted Allelic Frequency
(Expected Ratio)
V Number of this Phenotype
Total Counted:
__100___
(Observed Number)
Actual Allelic Frequency
(Observed Ratio)*
e.g., Yellow, wrinkled ppss
* Actual Allelic Frequency (Observed Ratio)
= Number of this Phenotype Total Counted „i 100 kernels total counted
Discussion:
A. How well do the predicted results match the actual results in Table 3?
B. Based on the Punnett Square predictions, can a statement be made as to whether your hypotheses are supported or rejected? Which and why?
C. Dihybrid F1 crosses result in a predictable F2 progeny phenotypic frequency that holds true universally. Based on the Expected outcome, what is it?
D. If your results are not as expected why might there be differences?
E. What applications might this type of genetic investigation have? How might the information be applied medically?
Exercise 3: Chi-square and Hypothesis Testing
Results:
Table 4: ƒÓ2 Goodness of Fit Test for F2 Phenotypic Results from F1 Corn Cross
Phenotype Description of F2 Progeny from Table 9.3 Observed Number from Table 9.3 Observed Ratio
from Table 9.3 Expected Ratio
from Table 9.3 * Expected Number,
calculated ** [Observed No. ¡V Exp. No.]2
„i Expected No.
e.g., Yellow, wrinkled
„¸ Sum of
column = ƒÓ2, Chi-square value *** >
* Expected Number, calculated
= „¸ Sum of Observed Number x Expected Ratio for that phenotype
** = (Observed number ¡V Expected number, calculated) square
„i Expected Number, calculated
*** ƒÓ2, Chi-square value = „¸ Sum of (Observed number ¡V Expected number, calculated)squared „i Expected Number, calculated
ƒÓ2 Table of Probabilities
Good Fit Probability Poor Fit Probability
Degrees of Freedom .90 .70 .60 .50 .20 .10 .05 .01
1 .02 .15 .31 .46 1.64 2.71 3.85 6.64
2 .21 .71 1.05 1.39 3.22 4.60 5.99 9.21
3 .58 1.42 1.85 2.37 4.64 6.25 7.82 11.34
4 1.06 2.20 2.78 3.36 5.99 7.78 9.49 13.28
Table 5: Summarization of ƒÓ2 Good Fit Results for F1 Corn Cross
ƒÓ2 value from Table 9.4 =
Value at 3 Degrees of Freedom that is closest to ƒÓ2 value =
What is the Fit Probability at the top of the column in which the value was found?
What is the % of probability that the observed results match the expected results?
(Multiply Fit Probability by 100)
Reading at the top of the Table, this Fit Probability indicates that the expected results hypothesis is a Good Fit Poor Fit
Circle the correct choice above
Discussion:
A. What can be concluded about your prediction of expected F2 progeny phenotypic outcome from the F1 cross? Was it close to the observed outcome?
B. How might the ƒÓ2 test for fitness be used in other ways? Try it on the tobacco seedling F1 cross, for instance.
C. In a typical cross where a parent with a completely dominant trait is mated with a parent exhibiting a completely recessive trait, what is the expected genotypic outcome and allelic frequency for the F1 progeny? Give an example.
D. In a typical cross where hybrid F1 parents are mated, what is the expected genotypic outcome and allelic frequency of the F2 progeny? Give an example.
E. For the F2 progeny produced from a typical F1 hybrid mating, how many totally recessive individuals would be produced if the progeny total population is six offspring? What if the progeny population was 20? 50? 1,000?
F. Excluding factors such as sex-linked genes, incomplete dominance or epistasis, etc., will the above cross results vary if different organisms are used, such as dogs or tulips? Why or why not?
G. How will factors such as sex-linked genes, incomplete dominance, or epistasis, etc., affect the expected outcomes that were investigated above?
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