Set up and complete Punnett squares for each of the following crosses: (remember Y = yellow, and y = blue)

Experiment 1: Punnett square crosses

















Procedure
1. Set up and complete Punnett squares for each of the following crosses: (remember Y = yellow, and y = blue)
Y Y and Y y Y Y and y y






a) What are the resulting phenotypes?


b) Are there any blue kernels? How can you tell?

2. Set up and complete a Punnett squares for a cross of two of the F₁ from 1b above:
a) What are the genotypes of the F₂ generation?

b) What are their phenotypes?

c) Are there more or less blue kernels than in the F₁ generation?

3. Identify the four possible gametes produced by the following individuals:
a) YY Ss:
b) Yy Ss:


c) Create a Punnett square using these gametes as P and determine the genotypes of the F₁:



d) What are the phenotypes? What is the ratio of those phenotypes?


4. You have been provided with 4 bags of different colored beads. Pour 50 of the blue beads and yellow beads into beaker #1 and mix them around. Pour 50 of the red beads and green beads in beaker #2 and mix them.





· #1 contains beads that are either yellow or blue.
· #2 contains beads that are either green or red.
· Both contain approximately the same number of each colored bead.
· These colors correspond to the following traits (remember that Y/y is for kernel color and S/s is for smooth/wrinkled):
· Yellow (Y) vs. Blue (y) Green (S) vs. Red (s).
A. Monohybrid Cross: Randomly (without looking) take 2 beads out of #1.
· This is the genotype of individual #1, record this information. Do not put those beads back into the beaker.
· Repeat this for individual #2. These two genotypes are your parents for the next generation. Set up a Punnett square and determine the genotypes and phenotypes for this cross.
· Repeat this process 4 times (5 total). Put the beads back in their respective beakers when finished.
a) How much genotypic variation do you find in the randomly picked parents of your crosses?

b) How much in the offspring?



c) How much phenotypic variation?

d) Is the ratio of observed phenotypes the same as the ratio of predicted phenotypes? Why or why not?

e) Pool all of the offspring from your 5 replicates. How much phenotypic variation do you find?

f) What is the difference between genes and alleles?
g) How might protein synthesis execute differently if there a mutation occurs?

h) Organisms heterozygous for a recessive trait are often called carriers of that trait. What does that mean?

i) In peas, green pods (G) are dominant over yellow pods. If a homozygous dominant plant is crossed with a homozygous recessive plant, what will be the phenotype of the F₁ generation? If two plants from the F₁ generation are crossed, what will the phenotype of their offspring be?




B. Dihybrid Cross: Randomly (without looking) take 2 beads out of beaker #1 AND2 beads out of beaker #2.

· These four beads represent the genotype of individual #1, record this information.
· Repeat this process to obtain the genotype of individual #2.
a) What are their phenotypes?

b) What is the genotype of the gametes they can produce?

· Set up a Punnett square and determine the genotypes and phenotypes for this cross.

c) What is your predicted ratio of genotypes? Hint: think back to our example dihybrid cross



· Repeat this process 4 times (for a total of 5 trials).

d) How similar are the observed phenotypes in each replicate?

e) How similar are they if you pool your data from each of the 5 replicates?

f) Is it closer or further from your prediction?



g) Did the results from the monohybrid or dihybrid cross most closely match your predicted ratio of phenotypes?

h) Based on these results; what would you expect if you were looking at a cross of 5, 10, 20 independently sorted genes?

i) Why is it so expensive to produce a hybrid plant seed?



j) In certain bacteria, an oval shape (S) is dominant over round and thick cell walls (T) are dominant over thin. Show a cross between a heterozygous oval, thick cell walled bacteria with a round, thin cell walled bacteria. What are the phenotype of the F₁ and F₂ offspring?


5. The law of independent assortment allows for genetic recombination. The following equation can be used to determine the total number of possible genotype combinations for any particular number of genes:
2^g= Number of possible genotype combinations (where “g” is the number of genes)
1 gene: 2¹= 2 genotypes
2 genes: 2²= 4 genotypes
3 genes: 2³ = 8 genotypes

Consider the following genotype:
Yy Ss Tt
We have now added the gene for height: Tall (T) or Short (t).
a) How many different gamete combinations can be produced?



b) Many traits (phenotypes), like eye color, are controlled by multiple genes. If eye color were controlled by the number of genes indicated below, how many possible genotype combinations would there be?

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