Mendelian Genetics

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Pre-Lab Questions

1. In a species of mice, brown fur color is dominant to white fur color. When a brown mouse is crossed with a white mouse all of their offspring have brown fur. Why did none of the offspring have white fur?

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2. Can a person’s genotype be determined by their phenotype? Why or why not?

3. Are incomplete dominant and co-dominant patterns of inheritance found in human traits? If yes, give examples of each.

4. Consider the following genotype: Yy Ss Hh. We have now added the gene for height: Tall (H) or Short (h).

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 in the following scenarios?

5 Eye Color Genes:

10 Eye Color Genes:

20 Eye Color Genes:

Experiment 1: Punnett Square Crosses

Procedure:

Part 1: Punnett Squares

1. Set up and complete Punnett squares for each of the following crosses: (remember = yellow, and y = blue). Please use the following example of a Bb and Bb cross as a guide for filling in your Punnett Squares:

Bb/BbBb
BBBBb
bBbbb

Cross #1:

YY/YyClick here to enter text.Click here to enter text.
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Cross #2:

YY/yyClick here to enter text.Click here to enter text.
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a. What are the resulting phenotypes?

Cross #1: Cross #2:

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 Cross #2 (above).

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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:

IndividualYY SsYy Ss
Gamete #1Click here to enter text.Click here to enter text.
Gamete #2Click here to enter text.Click here to enter text.
Gamete #3Click here to enter text.Click here to enter text.
Gamete #4Click here to enter text.Click here to enter text.

a. List the genotypes of the F1 generation that result from a cross of these two individuals.

b. What are the phenotypes of the F1 generation? What is the ratio of those phenotypes?

Part 2: Monohybrid Cross

Table 1: Parent Genotypes: Monohybrid Crosses

GenerationGenotype of Individual #1Genotype of Individual #2
PClick here to enter text.Click here to enter text.
P1Click here to enter text.Click here to enter text.
P2Click here to enter text.Click here to enter text.
P3Click here to enter text.Click here to enter text.
P4Click here to enter text.Click here to enter text.

Table 2: Generations Data Produced by Monohybrid Crosses

ParentsPossible Offspring GenotypesPossible Offspring Phenotypes
PClick here to enter text.Click here to enter text.
P1Click here to enter text.Click here to enter text.
P2Click here to enter text.Click here to enter text.
P3Click here to enter text.Click here to enter text.
P4Click here to enter text.Click here to enter text.

Post-Lab Questions

1. How much genotypic variation do you find in the randomly picked parents of your crosses?

Homozygous Dominant:

Heterozygous:

Homozygous Recessive:

2. How much genotypic variation do you find in the offspring?

Homozygous Dominant:

Heterozygous:

Homozygous Recessive:

3. How much phenotypic variation do you find in the randomly picked parents of your crosses?

Yellow:

Blue:

4. How much phenotypic variation do you find in the offspring?

Yellow:

Blue:

5. The predicted phenotypic ratio for a heterozygous cross is 3:1 yellow:blue. Would you expect the phenotypic ratio for your offspring to be similar? Why or why not?

6. What is the difference between genes and alleles?

7. How might protein synthesis execute differently if a mutation occurs?

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

9. In peas, green pods (G) are dominant over yellow pods (g). 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?

Part 3: Dihybrid Cross

Table 3: Parent Genotypes: Dihybrid Crosses

GenerationGenotype of Individual #1Genotype of Individual #2
PClick here to enter text.Click here to enter text.
P1Click here to enter text.Click here to enter text.
P2Click here to enter text.Click here to enter text.
P3Click here to enter text.Click here to enter text.
P4Click here to enter text.Click here to enter text.

Table 4: Generation Data Produced by Dihybrid Crosses

ParentsPossible Offspring GenotypesPossible Offspring PhenotypesGenotype RatioPhenotype Ratio
PClick here to enter text.Click here to enter text.Click here to enter text.Click here to enter text.
P1Click here to enter text.Click here to enter text.Click here to enter text.Click here to enter text.
P2Click here to enter text.Click here to enter text.Click here to enter text.Click here to enter text.
P3Click here to enter text.Click here to enter text.Click here to enter text.Click here to enter text.
P4Click here to enter text.Click here to enter text.Click here to enter text.Click here to enter text.

Post-Lab Questions

1. How similar are the observed phenotypes in each replicate?

2. How similar are they if you pool your data from each of the five replicates?

3. Is it closer or further from your prediction?

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

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

6. Why is it so expensive to produce a hybrid plant seed?

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

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