BI 101-700 CRITICAL THINKING ASSIGNMENT

11 Jun BI 101-700 CRITICAL THINKING ASSIGNMENT

Question
BI 101-700 CRITICAL THINKING ASSIGNMENT

LAB: STUDYING PEDIGREES CONCERNING THE INHERITANCE OF LACTOSE INTOLERANCE (Adapted from Howard Hughes Medical Institute – www.biointeractive.org)

BACKGROUND INFORMATION

A defining characteristic of mammals is that mothers produce milk for their infants through a process called lactation. “Mother’s milk” is packed with the proteins, fats, and carbohydrates that support the baby’s growth and development. The main carbohydrate in milk is the sugar lactose, which is a disaccharide.

Infant mammals produce the enzyme lactase in their small intestines, which breaks down lactose into glucose and galactose. The two simpler sugars, or monosaccharides, are easily absorbed through the small intestine and then into the bloodstream. The blood delivers the sugars throughout the body to provide cells with a source of energy.

At around the time children stop drinking their mother’s milk, most of them also stop producing lactase. If lactase is not produced and a person drinks milk, undigested lactose travels from the small intestine to the large intestine, where it is digested by bacteria. When this happens, a person could have abdominal pain, bloating, flatulence, and diarrhea. Individuals with these symptoms are lactose intolerant.

Only a minority of human adults—35% of the global human population—continues to produce lactase into adulthood. These individuals are lactase persistent, meaning that lactase production persists beyond childhood. (They are also usually lactose tolerant, meaning that they don’t have any problems when they drink milk.)

Genetic studies suggest that lactose tolerance arose among human populations in the last 7,000 to 9,000 years. This is also when humans began domesticating animals like cows, goats, and camels and started drinking their milk.

LEARNING OBJECTIVES:

After doing this online lab exercise the student will be able to:

1. Understand and be able to describe what type of disorder lactose intolerance is.

2. Compare and analyze different pedigrees. Be able to distinguish a pedigree that shows a sex-linked trait from one that shows an autosomal trait. Predict what a pedigree of a dominant trait would look like in comparison to one showing a recessive trait. Be able to explain the difference between these methods of inheritance.

3. Demonstrate critical thinking; this means thinking that is purposeful and leads to reasoned judgments. The student will do this by showing that by applying the use of Punnett Squares one is able to interpret pedigrees.

4. Formulate a valid generalization or conclusion about the form of inheritance of lactose intolerance, based on the information learned from the pedigrees.

NOTE: You will be graded with a specific rubric developed for this lab.

You will find the rubric at the end of the lab.

PROCEDURE

Part 1:

Watch the following short video to get some background information on lactase:

http://media.hhmi.org/biointeractive/films/Got_Lactase.html

Identify the major ideas presented in the video and write a brief paragraph for each of the 4-5 most important concepts. This should not be a list, but rather a description of each concept.

1. Write your short essay in the space below.

2. What idea(s) did you find MOST interesting? Why?

3. What questions about lactase do you still have after watching the video?

Part 2:

Determining the Pattern of Inheritance of Lactose Tolerance/Intolerance

To determine how lactose tolerance/intolerance is inherited, researchers examined nine extended Finnish families for five generations.

Below is one of those pedigrees. Look at this pedigree and then answer the questions below. (For a refresher on pedigrees, refer to the sample pedigree at the end of the lab).

Figure 2. Pedigree of Family A. (Adapted from a figure in Enattah, N. S., et al. 2002 Nature Genetics 30: 233-237.)

QUESTIONS:

1. Based on the pedigree above, which of the following terms are appropriate for describing the inheritance of the lactose-intolerance trait (filled-in symbols)? Check all that apply.

____ Inherited ____ Not inherited

____ Dominant ____ Recessive

____ Autosomal ____ X-linked

2. Provide at least two pieces of evidence in support for the choice(s) you made in question #1. Use Punnett squares as supporting evidence and circle the important information.

3. Draw a logical conclusion about how lactose intolerance is inherited, based on the pedigree above.

4. How comfortable are you with drawing a firm claim about the inheritance of lactose intolerance? What might you do next to increase your confidence in making this claim?

5. Study Individuals 5 and 6 of Generation III in Family A and their child. The two parents are lactose tolerant, yet their son is lactose intolerant. Is this data consistent or inconsistent with the claim you made in question 3? Explain your answer using a Punnett square and circle the appropriate evidence.

You are now going to examine three additional pedigrees from the Finnish study.

Figure 3. Pedigrees of Families B, C, and D. (Adapted from a figure in Enattah, N. S., et al. 2002 Nature Genetics 30: 233-237.)

6. Does the data presented in these additional pedigrees support your own claim stated in #3 above? Explain your answer fully.

7. Based on your claim, what is the genotype of Individual 3, Generation IV in Family C? Explain your answer fully.

8. Based on the same claim, what is the genotype of the father of Individual 4, Generation IVin Family D? Explain your answer fully.

9. Individuals 8 and 9, Generation IV in Family B are sisters. Based on your inheritance claims, what is/are the possible genotype(s) of:

a. Individual 9? _____

b. Individual 8? _____

c. The parents of Individuals 8 and 9? _________

10. Individual 4, Generation IV in Family B is the sister of Individuals 8 and 9 in the question above. What is the probability that Individual 4 is homozygous? ______________ Heterozygous? _________