Provide at least 2 pieces of evidence in support for the choice you made in question no 1. Use punnet squares as supporting evidence and circle the important information. It is question no 2. Due date is tonight in 2 hours.
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
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. A very interesting, and informative documentary. It starts off by explaining what is lactase and what it
does. Lactase is an enzyme found in the lining of the small intestine that acts as a catalyst in the breakup
of lactose into glucose and galactose, which are easily digested by the body. It was surprising to watch
that in most people the gene for lactase, the enzyme that digests lactose, is switched on at birth and
switched off at the age of weaning or in certain cases at the age of 2. So, how come some people are
lactose tolerant (persistence) for the rest of their life, while others are not.
The summary of the documentary is to find out how does lactose persistence come about and why does it
occur in only 35% of the world?s population. This is the reason behind narrator and geneticist Spencer
Wells visit to University of College in London. A simple test of drinking milk in which if one?s glucose
levels increase sharply can show if one is lactose persistent. However, upon further imploring, data shows
that for some reason people of European descent are more likely to be lactose tolerant. One must ask, is
there is a link between one?s Background, upbringing or genetic reason behind being lactose persistence.
Further exploring of the DNA prove that genetic mutation cause lactase persistence. Mutations occur not
only in coding regions of genes but also in the regulatory regions that determine when and where a gene is
turned on. All known mutations giving rise to lactase persistence are in a genetic ?switch? that regulates
expression of the lactase gene. Also, there are multiple mutations in different parts of the world. Per the
film, lactose tolerance and practice of dairying rose at the same time in different parts of the world.
The film concludes that lactose tolerance or intolerance is a genetic trait. Archeological evidence of using
milk matches indicates that pastoralist populations were using milk 5-9 thousand years ago. DNA
evidence indicates that mutations in the lactase gene arose in milk-drinking populations at the same time. 2 What idea(s) did you find MOST interesting? Why? The most interesting idea for me was that it is no co-incidence that cultures and regions in which cows,
and sheep?s, were raised had more lactose tolerant population. This proves how genetic traits are passed
down. Also, how George Mendel?s work on how heredity became the basis of genetics.
I was truly fascinated by how as kids most of us can drink milk, but after the age of 2 so many become
I was surprised to find out that only 35% of the world is lactose persistence. Clearly, this shows as a
human race we have not mutated enough. Also, I understand the difference between milk allergy and
3 What questions about lactase do you still have after watching the video? My question is what is the recommended dosage for lactase for an average person. Also, can lactose
intolerance appear suddenly or at older age.
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: 233237.) 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. __X__ Inherited __X__ Not inherited __X__ Dominant ____ Recessive ___X_ 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 IV
in 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? ______________
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