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Solved by a verified expert:Experiment 1: Punnett
Square Crosses
In this experiment you will use
monohybrid and dihybrid crosses to predict patterns of inheritance.

Materials

(2) 100 mL Beakers
Permanent Marker

Procedure:
Part 1: Punnett Squares

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

What are the resulting phenotypes?

Are there any blue kernels? How can you tell?

Set up and complete a Punnett squares for a cross of two of the F1
from Step 1 (above).

What are the genotypes of the F2 generation?

What are their phenotypes?

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

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 the
ratio of those phenotypes?
Part 2 and 3 Setup

Use the permanent marker to label the two 100 mL beakers as “1” and
“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.
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 the
experiment:
·
Beaker 1 contains beads that are either
yellow or blue.
·
Beaker 2 contains beads that are either
green or red.
·
Both beakers 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):
1.
Yellow (Y) vs. Blue (y)
2.
Green (G) vs. Red (g).
Part 2: Monohybrid Cross

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

Repeat Step 1 for Individual #2. These two genotypes represent the
parents (generation P) for the next generation.
Set up a Punnett square and determine the genotypes and phenotypes
for this cross. Record your data in Table 2
Repeat Steps 1 – 2 four more times (for a total of five subsequent
generations). Return the beads to their respective beakers when finished. Then,
complete Table 2.

Table 2:Generation Data Produced by Monohybrid
Crosses

Parents

Possible Offspring
Genotypes

Possible Offspring
Phenotypes

Genotype Ratio

Phenotype Ratio

P

P1

P2

P3

P4

Part 3: Dihybrid Cross

Randomly (without looking) remove two beads from of Beaker 1 and
two beads from Beaker 2. These four beads represent the genotype of
Individual #1. Record this information in Table 3
Repeat Step 1 to obtain the genotype of Individual #2. Record the
phenotypes of both individuals in Table 3.

Table 3:Parent Genotypes: Dihybrid Crosses

Generation

Genotype of Individual 1

Genotype of Individual 2

P

P1

P2

P3

P4

Determine what the possible genotypes might be if each individual
produced gametes. Record these possible genotypes in Table 4.
Predict the ratio of possible genotypes which could be produced by a
cross between Individual #1 and Individual #2? Record your predictions in
Table 4
Hint: Think back to the example the dihybrid cross in the
Introduction. Record your prediction in Table 2.
Set up a Punnett square and determine the genotypes and phenotypes
for this cross.
Repeat Step 5 four additional times (for a total of five subsequent
generations).

Table 4:Generation Data Produced by Dihybrid
Crosses

Parents

Possible Offspring
Genotypes

Possible Offspring
Phenotypes

Genotype Ratio

Phenotype Ratio

P

P1

P2

P3

P4

Post-Lab Questions

Part 2: Monohybrid Cross

How much genotypic variation do you find in the randomly picked

How much in the offspring?

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

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

What is the difference between genes and alleles?

How might protein synthesis execute differently if a
mutation occurs?

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

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 F1generation? If two plants
from the F1generation are crossed,
what will the phenotype of their offspring be?

Part 3: Dihybrid Cross

How similar are
the observed phenotypes in each replicate?

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

Is it closer or

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

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

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

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 phenotype of the F1and F2offspring?