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Question

Experiment 1: Punnett SquareCrossesIn this experiment you will usemonohybrid and dihybrid crosses to predict patterns of inheritance.

Materials   Blue Beads Green Beads Red Beads	Yellow Beads (2) 100 mL Beakers Permanent Marker

Procedure:

Part 1: Punnett Squares

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

1. What are the resulting phenotypes?
2. Are there any blue kernels? How can you tell?
3. Set up and complete a Punnett squares for a cross of two of the F₁ from Step 1 (above).
4. What are the genotypes of the F₂ generation?
5. What are their phenotypes?
6. Are there more or less blue kernels than in the F₁ generation?
7. 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:

What are the phenotypes? What is theratio of those phenotypes?

Part 2 and 3 Setup

1. Use the permanent marker to label the two 100 mL beakers as "1" and "2".
2. Pour 50 of the blue beads and 50 of the yellow beads into Beaker 1. Sift or stir the beads around to create a homogenous mixture.
3. Pour 50 of the red beads and 50 of the green beads into Beaker 2. Sift or stir the beads around to create a homogenous mixture.

Assumptions for the remainder of theexperiment:

• Beaker 1 contains beads that are eitheryellow or blue.

• Beaker 2 contains beads that are eithergreen or red.

• Both beakers contain approximately thesame number of each colored bead.

• These colors correspond to thefollowing traits (remember that Y/y is for kernel color and S/s is forsmooth/wrinkled):

1.     Yellow (Y) vs. Blue (y)

2.     Green (G) vs. Red (g).

Part 2: Monohybrid Cross

1. Randomly (without looking) take two beads out of Beaker 1. This is the genotype of Individual #1. Record the genotype in Table 1. Do not put these beads back into the beaker.

Table 1: Parent Genotypes: Monohybrid Crosses
Generation	Genotype of Individual 1	Genotype of Individual 2
P
P1
P2
P3
P4

 

1. Repeat Step 1 for Individual #2. These two genotypes represent the parents (generation P) for the next generation.

    

2. Set up a Punnett square and determine the genotypes and phenotypes for this cross. Record your data in Table 2

    

3. Repeat Step 3 four more times (for a total of five subsequent generations). Return the beads to their respective beakers when finished.

    

 

Table 2: Generation Data Produced by Monohybrid Crosses
Parents	Possible Offspring Genotypes	Possible Offspring Phenotypes	Genotype Ratio	Phenotype Ratio
P
P1
P2
P3
P4

Post-Lab Questions

Part 2: Monohybrid Cross

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

1. How much in the offspring?

1. How much phenotypic variation?

1. Is the ratio of observed phenotypes the same as the ratio of predicted phenotypes? Why or why not?

1. Pool all of the offspring from your five replicates. How much phenotypic variation do you find?

1. What is the difference between genes and alleles?

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

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

1. 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 F₁generation are crossed, what will the phenotype of their offspring be?