Download Genetic Corn Lab - District 196 e

Genetic Corn Lab
Purpose: To discover Mendel’s principles involving monohybrids.
Introduction: Maize (or corn) is a plant product of great importance to our nutritional well-being but also to our
understanding of genetics. Pioneers like Barbara McClintock used corn to discover many new and puzzling genetic facts.
The corn that you will be studying represents the second filial generation (F2) of a cross between two purebred plants.
Each kernel (seed) on an ear of corn is a separate offspring of a cross between female parent and male parent sex cells.
The silk are hair-like parts known as the stigma and are a part of the plant’s female reproductive parts that pollen from the
male tassel can attach to as it flies through the air. The pollen produces a pollen tube that travel down the stigma and into
the ovule chamber which will contains an egg that the pollen sperm will fertilize. Following fertilization, these resulting
seeds (offspring) develop on the “cob” and each seed could be planted to produce an entire new corn plant. Each cob has
about 200-400 seeds or offspring.
In producing the genetic corn the plant breeder selected purebred parents. In this case, a purebred, purple seed- producing
parent was crossed with a purebred, non-purple (yellow) seed-producing parent. By placing pollen from one of the
parents onto the silk of the other parent, the breeder produced kernels that are called the first filial (F1) generation. These
seeds were planted and grew into the next generation of mature corn plants. The breeder then placed the pollen from an
F1 plant onto the silk of a different F1 plant. The progeny of this cross are called the F2 generation and are represented by
the kernels on the ears you are using and seeing today.
Notice the corn kernels you are observing today also have at least two other obvious features. They are either wrinkled or
smooth and they are either indented or rounded on the edge. The indented feature is not easy to discern, especially on the
wrinkled seeds, but the wrinkled yellow and purple seeds are easy to observe.
Data table: Using a piece of tape to mark your spot, count all the seeds & fill in the data table below.
Your Group Data
Data Description
Kernel (seed) totals
Purple kernels
Data Description
Purple kernels
Purple & smooth
Purple & smooth
Purple & wrinkled
Purple & wrinkled
Yellow kernels
Yellow kernels
Yellow & smooth
Yellow & smooth
Yellow & wrinkled
Yellow & wrinkled
Total seeds counted
Total seeds counted
Calculate the percentage of
purple seeds
Calculate the percentage of
yellow seeds
Calculate the percentage of
purple seeds
Calculate the percentage of
yellow seeds
Calculate the nearest small
whole number ratio of purple
to yellow seeds
Class Data
Kernel (seed) totals
:
Calculate the nearest small
whole number ratio of purple
to yellow seeds
:
Hypothesis based on the data would be that: we would expect to find what ratio of seeds in the F2 generation of this
monohybrid cross dealing with the purple vs yellow seed color?
Analysis questions:
1) Choose appropriate symbols for the purple and non-purple (yellow) genes using the guidelines that the dominant gene is the
capital letter and the recessive gene is the same but lower case letter.
Purple color gene letter:
Yellow color gene letter:
2) What is the genotype of each of the parents of the F1 generation: __________________ & __________________
3) What is the phenotype of each of the parents of the F1 generation: __________________ & _________________
4) What is the genotype of each of the parents of the F2 generation: __________________ & __________________
5) What is the phenotype of each of the parents of the F2 generation: __________________ & _________________
6) What is the name of the type of cross that produced this F2 generation for the seed color trait?
7) Construct a Punnett square that shows the parental cross (w/ F1 offspring) and the F1 cross (w/ F2 offspring) that was discussed in
question 6. Gametes of each parent go outside top and left of the box (one letter per trait considered).
parental cross
monohybrid (F1) cross
8) Given the total number of offspring on your cob and using the expected probability for each of the seed color phenotypes as
determined by the experiment numbers from your data table or from the Punnett square above, Calculate the expected number of each
phenotype. (show work & circle answers)
Expected purple seeds:
Expected yellow seeds:
9) Determine the support for your hypothesis using the Chi-square evaluation for both your group data and the class data: (show
work & circle answers). # of categories _____________ d.f. = ________________ χ2 = Σ(o-e)2/e
Group Data: _________________________________
Calculated χ2 value vs table value
Class Data: _____________________________________
Calculated χ2 value vs table value
Did your data support the hypothesis? ___________________
Did class data support the hypothesis? ___________________
10) Which χ2 value (class or group) was smaller for most groups? What does this suggest about sample size and hypothesis
evaluation?
Genetic Corn Lab – Part 2
Purpose: To discover Mendel’s principles involving dihybrid crosses.
Introduction: The corn data you collected in the Part 1 data table will be used to determine how two different traits can be
analyzed when they are inherited simultaneously. Question: do these two genes get inherited together or do they act as if
they are inherited independently of each other. (Think how chromosomes behave in meiosis as you reflect on this
question.) Consider what your data would look like if the two genes were inherited:
a) as if they were on the same chromosome? (linked)
b) as if they were on different chromosomes? (independently assorted)
If you were to look at the original homozygous dominant (purple) parent ear of corn, you would realize that the
seeds were not only all purple but you might have noticed that each of those purple seeds were smooth as well.
Additionally, all of the homozygous recessive (yellow) parent seeds were also wrinkled.
If the genes for seed color are:
And the genes for seed texture are:
P = purple
S = smooth
p = yellow
s = wrinkled
1. Then what would be the homozygous parent genotypes? (remember diploid organisms have 2 letters per trait)
Homozygous purple, smooth ___________________
Homozygous yellow, wrinkled _________________
2. If you were to cross these two different parent gametes, we would need to know the kind of gametes each parent would
give. Therefore, write down the possible gametes of each parent. (remember gametes have 1 letter per trait)
Homozygous purple, smooth ___________________
Homozygous yellow, wrinkled _________________
3. What would the F1 generation seeds all have for a genotype for such a cross? _______________________
(you could do a Punnett square if you need to but you likely won’t have to)
4. What are the resulting F1 offspring called? (hint: 2 trait & heterozygous) ____________________________
5. After you planted these F1 seeds, the plants would grow and become sexually mature and you could cross any two
plants, what kind of a cross would this be called? ___________________________________________
6. List each of the kinds of gametes each of the dihybrids could produce for such a cross?
__________________________________________________________________________________________
7. Build a Punnett square on the back that shows a dihybrid cross for these two traits. Identify your work for each letter
by boxing the answer within a box clearly marked on the outside with the letter below. If you prefer, when appropriate,
create a new data table on the back and label it with the appropriate letters.
a) determine the phenotypic ratios from the Punnett square for each of the 4 F2 generation categories.
b) the ratios of each phenotype will help you calculate the expected numbers of each you should expect
to get from a such a cross for both your data and the class data.
c) from the date table on the previous corn lab - part 1 sheet - get the 4 F2 generation types which would
be observed and use them to get the observed for each of the 4 types of phenotypes.
d) calculate the χ2 value for your group and the class data.
e) evaluate what the χ2 value with respect to the degrees of freedom and suggest whether your group and class
data support the hypothesis that these genes assort independently of each other.
Only consider (f) below if you are looking for an additional challenge:
f) for you very bright types, what would the data look like, do you suppose, if the genes of these two
traits were inherited together (if they were linked on the same chromosome)?