This assignment was developed from “Pedigrees and the Inheritance of Lactase” from BiointeractiveLinks to an external site..
The enzyme
𝛽
-galactosidase or lactase is responsible for converting lactose sugar into glucose and galactose. 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 into the bloodstream. The blood delivers the sugars throughout the body to provide cells with a source of energy.
At around the time that 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—continue 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.
The film Got Lactase? The Co-evolution of Genes and CultureLinks to an external site. traces the evolution of lactose tolerance. It also describes how researchers analyzed the pedigrees of several Finnish families to identify the changes in the DNA, or mutations, responsible for this trait.
In this discussion, you will analyze some of those pedigrees to determine how the lactose-tolerant trait is inherited.
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 the pedigree and then answer the questions below. This video explains the symbolsLinks to an external site. of a pedigree.
Figure 2. Pedigree of Family A. (Adapted from a figure in Enattah, N. S., et al. 2002 Nature Genetics 30: 233-237.)
Discussion Assignment
Examine Generation III, Individuals 1, 2, and their offspring. What type of inheritance do you believe lactose intolerance must be? Is it dominant, recessive, or X-linked? How certain can you be? Explain your thought process.
Now, look at Generation IV, Individuals 5 and 6, and their offspring. Does the inheritance pattern fit this generation? Why or why not?
Look at the whole pedigree and see if you can determine the inheritance pattern.
Review your classmate’s posts. After reading their analyses, have you changed your mind? Comment to a classmate with a question or an explanation. Is there another example in the pedigree that you think provides evidence of the type of inheritance?
Grading Rubric
Student describes the type of inheritance pattern- 5 points
Student explains their analysis and how they came to their inheritance pattern determination – 10 points
Student Replies to a classmate with substantive information – 5 points
Grammar and Punctuation – 5 points
