Genetics & Genomics

Exercise 1 Punnett Squares

In this exercise, you will use Punnett squares to determine the probabilities of offspring in four different scenarios.

Note: View the following video for a demonstration of drawing, making, and using a Punnett Square before continuing the procedures.

If needed, a descriptive text transcript is available.

Drawing, Making, and Using a Punnett Square

 

Procedure

1. Describe the following four scenarios by drawing Punnett squares. You will upload photos of your drawings into Punnet Square 1 – 4. Refer to the information found in the background section as needed.
2. Answer the questions at the bottom of the page using the Punnett squares that you have created.

Scenario 1: Cystic Fibrosis

Dominant (F): normal; no cystic fibrosis

Recessive (f): cystic fibrosis

A woman has a history of cystic fibrosis in her family and found out that she has the gene for cystic fibrosis but is not affected by the gene. Her husband also has a history of cystic fibrosis in his family. He got tested yesterday and found that he is also a carrier for the disease but is not affected by it. First, list the genotype of the mother and father in Data Table 1. Then, draw a Punnett square for their offspring on a piece of paper. Be sure to include your name and the date with your drawing. Take a photo of the completed Punnett square and upload the image into Punnett Square 1.

Scenario 2: Tay-Sachs

Dominant (T): normal; no Tay-Sachs

Recessive (t): Tay-Sachs

A man is a carrier for Tay-Sachs. He is going to have a child with a woman who has homozygous dominant genes. First, list the genotype of the mother and father in Data Table 2. Then, draw a Punnett square for their offspring on a piece of paper. Be sure to include your name and the date with your drawing. Take a photo of the completed Punnett square and upload the image into Punnett Square 2.

Scenario 3: Huntington’s and Cystic Fibrosis

Dominant (H): Huntington’s disease                           Dominant (F): normal; no cystic fibrosis

Recessive (h): normal; no Huntington’s                      Recessive (f): cystic fribrosis

A man with a heterozygous genotype for Huntington’s disease is also a carrier for cystic fibrosis. His wife has cystic fibrosis but does not have Huntington’s disease. First, list the genotype of the mother and father in Data Table 3. Then, draw a Punnett square for their offspring on a piece of paper. Be sure to include your name and the date with your drawing. Take a photo of the completed Punnett square and upload the image into Punnett Square 3.

Scenario 4: Color Blindness

X-linked dominant trait: no color blindness

X-linked recessive trait: color blindness

A color-blind man marries a woman who is not color blind, nor is she a carrier for color blindness. First, list the genotype of the mother and father in Data Table 4. Then, draw a Punnett square for their offspring on a piece of paper. Be sure to include your name and the date with your drawing. Take a photo of the completed Punnett square and upload the image into Punnett Square 4.

Exercise 1 – Questions

Question 1

Scenario 1: Cystic Fibrosis

1. What is the percentage likelihood that the couple will have a child with cystic fibrosis?

 

Question 2

2. What is the percentage likelihood that the couple will have a child that has the allele for cystic fibrosis?

 

Question 3

3.  If the parents have two children without the disorder, what is the probability that their third child will have cystic fibrosis?

 

Question 4

Scenario 2: Tay-Sachs

4. What is the percentage likelihood that the couple will have a child who has the phenotype for Tay-Sachs disease?

 

 

Question 5

5. What is the percentage likelihood that the couple will have a child who is a carrier for Tay-Sachs disease?

 

Question 6

Scenario 3: Huntington’s and Cystic Fibrosis

6. What is the percentage likelihood that the couple will have a child who has both Huntington’s disease and cystic fibrosis?

 

Question 7

7. What is the percentage likelihood that the couple will have a child who has neither Huntington’s disease nor cystic fibrosis?

 

Question 8

8. What is the percentage likelihood that the couple will have a child who is a carrier for cystic fibrosis?

 

Question 9

Scenario 4: Color Blindness

9. What is the percentage likelihood that the couple will have a son who is also color blind?

 

Question 10

10. If the couple has a daughter, what is the percentage likelihood that the daughter will be a carrier for color blindness?

 

 

 

 

 

 

Exercise 2 Pedigree Charts

In this exercise, you will read pedigree charts, and you will select the chart that best represents hemophilia, a sex-linked recessive trait.

Procedure

1. Read the following scenario:

Hemophilia is a sex-linked recessive trait with a long, well-documented history in European royal families. The allele for this disease is located exclusively on the X chromosome.

1. Examine the three pedigree charts and determine which of the following three pedigree charts best matches the scenario.

Legend:

 

 

 

 

 

 

 

 

 

Chart 1:

Chart 2:

 

 

 

 

 

 

 

Chart 3:

Exercise 2 – Questions

Question 1

1. Which pedigree chart best represents the spread of hemophilia?

 

Question 2

2. How would the chart differ if the father in generation 1 had the disease?

 

 

 

 

 

 

 

 

 

 

Exercise 3 Karyotyping

In this exercise, you will investigate a series of karyotypes, and identify and describe the diseases that are associated with the karyotypes.

Procedure

1. Compare the karyotype of a healthy human to the karyotypes of three chromosomal disorders.

Image copyright Alila Medical Images, 2013. Used under license from Shutterstock.com.Normal (Healthy Human).

Image copyright Alila Medical Images, 2013. Used under license from Shutterstock.com.Disorder 1.

Image copyright Alila Medical Images, 2013. Used under license from Shutterstock.com.Disorder 2.

Image copyright Alila Medical Images, 2013. Used under license from Shutterstock.com.Disorder 3.

1. For Disorder 1, describe the chromosomal abnormality. For example, a genotype may be described as having “two Y chromosomes” or “an extra copy of chromosome 14.” Record your findings in the “Genotype” column of Data Table 5.
2. Based on the genotype, determine the name of Disorder 1. Refer to Table 3 of the Background as necessary. Record the name in the “Chromosomal Disorder” column of Data Table 5.
3. List the symptoms of Disorder 1 in the “Phenotype” column of Data Table 5.
4. Repeat steps 2-4 for Disorder 2 and Disorder 3.

Exercise 3 – Questions

Question 1

1. How are an individual’s chromosomes karyotyped?

Question 2

2.  How does nondisjunction occur? What happens to the gametes that are a product of nondisjunction?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Exercise 4 The Human Genome Project

In this exercise, you will research the Human Genome Project using the Internet.

Procedure

1. Conduct online research related to the Human Genome Project. List your resources in Data Table 6.
2. Write a paragraph about the Human Genome Project in Data Table 6. Include the following information and any additional relevant information that you discover in your research:
   1. The project starting and ending dates.
   2. The entities (i.e. countries and/or organizations) that led the Human Genome Project.
   3. The major goals of the project.

Exercise 4 – Questions

Question 1

1. Approximately how many genes are present in the human body?

 

Question 2

2. How has the Human Genome Project impacted human medicine?