Mendelian Genetics

Activity

The laws of segregation, independent assortment, and dominance form the basis of all genetics. The ability to predict the results of crossing experiments and explain any variance between expected and observed results is still a vital part of our understanding of heredity. In this lab assignment you will experiment with monohybrid crosses and explore the role of chance in genetics.

Experiment 1

Questions

1. (10 points)

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

· Y Y and Y y

Parent 1

Y

Y

Parent 2

Y

YY

YY

y

Yy

yy

· Y Y and y y

Parent 1

Y

Y

Parent 2

Y

Yy

Yy

y

Yy

Yy

b. What are the resulting phenotypes for each cross? Are there any blue kernels?

Y Y and Y y

Y Y and y y

The resulting phenotypes is that all the offsprings are yellow because all the offspring have at least one Y (yellow, dominant) allele

All the offsprings are yellow

There are no blue kernels in either cross and all are yellow because the genotypes of all the kernels have at least one dominant (Y) gene which codes for yellow color.

2. (10 points)

a. Set up and complete a Punnett squarefor a cross of two of the F1 from the Y Y and y y cross above.

Parent 1

Y

Y

Parent 2

y

Yy

Yy

y

Yy

Yy

b. What are the genotypes and phenotypes of the F2 generation?

The genotypes of offsprings are Yy (heterozygous) and their proportion is 100% If Y= yellow an y= blue, then the phenotypes of the off springs would be the characteristics of Y gene which means all the off springs will have a yellow color.

Experiment 2

Questions

As you select the beads from the beaker, complete this table with each cross. You may complete the associated Punnett Squares on paper, but do not need to submit them as part of this lab.

Parents – randomly selected

F1 – determined from Punnett square

Cross

Genotype parent #1

Genotype parent #2

4 Genotypes

4 Phenotypes

1

yy

yy

yy

yy

2

Yy

yY

YY

Yy

3

Yy

YY

YY

YY

4

yY

yy

Yy

yy

5

yy

YY

Yy

Yy

1. (10 points)

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

Possible Genotype

Parents

Offspring

YY

3

4

Yy

3

10

yy

4

6

Total

10

20

b. How much phenotypic variation do you find in the parents of your crosses? How much in the offspring?

2. (10 points)

a. What is the ratio of phenotypes (yellow kernel color: blue kernel color) in the 20 offspring of your five crosses?

b. If you were to run this experiment 1000 times, rather than just 5 times, what would you expect the ratio of phenotypes to be in the offspring?

c. Is the ratio of observed phenotypes the same as the ratio of predicted phenotypes in the offspring? Why or why not?

3. Organisms heterozygous for a recessive trait are often called carriers of that trait. Explain what this means. (10 points)