A sickeningly sweet baby boy

Lab 9: Follow the instructions and complete the assignment below. Submit your answers through the Lab 9 submission on Blackboard.

Lab 9 1

Lab 9. Inheritance 2

In this lab, we’ll be exploring inheritance again, but in humans. First, we’ll be looking at a real- life scenario of a known human disorder, and work through the family history to understand how the disorder works. Second, we’ll be exploring your own facial traits and seeing how inheritance works with a partner of your choice. EXERCISE 1 For this exercise, you’ll be exploring a real life scenario on inheritance in humans. A. Read the scenario below: A Sickeningly Sweet Baby Boy: A Case Study on Autosomal Recessive Inheritance by Jacqueline Washington, Department of Biology and Chemistry, Nyack College, Nyack, NY Anne Zayaitz, Department of Biology, Kutztown University, Kutztown, PA

Scenario: Emma and Jacob Miller were so excited at the birth of their baby Matthew.

Both the pregnancy and delivery had been uneventful. But in the back of their minds, they really were worried because their first child, Samuel, died at the age of nine days. By the fifth day after birth, Matthew began to have trouble nursing and by the seventh day he had completely stopped feeding. Emma and Jacob were frantic because it seemed to them that Matthew might also die. “What is going on with our family? Another sick baby?” Jacob thought to himself.

Emma and Jacob rushed him to the emergency room. Although Mathew’s limbs were rigid and he had had a seizure, the examination showed no infection and his x-rays were normal. The doctor also did routine lab tests on his blood and urine. “Doctor, do you think that this funny smell in Matthew’s diapers has anything to do with his problem?” Emma asked. “I brought one along so that you could smell it too.”

Matthew’s urine did have a sweet, maple syrup smell and lab results revealed elevated levels of the branched chain amino acids valine, isoleucine, and leucine. Skin biopsies from the baby and his parents were taken and cultured. The ability of the cultured skin fibroblasts to metabolize these three amino acids was determined. While his parents’ enzyme activity levels were nearly normal, Matthew’s was 200 times lower than normal.

“Given the medical information and the smell of the urine, Matthew has Maple Syrup Urine Disease (msud),” reported Dr. Morton of the Clinic for Special Children. “He will not be able to breast feed or drink regular formula. What is really important is that Matthew eats a low protein diet. This diet must continue for the rest of his life or else the amino acids will accumulate in the body creating a situation that leads to brain swelling, neurological damage, and death. In spite of dietary intervention, the disease may cause several complications, the most notable being mental retardation.”

Lab 9: Follow the instructions and complete the assignment below. Submit your answers through the Lab 9 submission on Blackboard.

Lab 9 2

A discussion with Emma’s grandmother revealed that Emma’s mother had two sisters who died in their first year of life; no one knew why. Jacob’s father had a brother who died at seven months of age from unknown causes. Could the gene for msud run in both of their families?

msud is due to a recessive gene. For an individual to be affected, he or she would need to inherit a defective nonworking copy from each parent. The individual would then be described as being homozygous recessive.

B. Now that you’ve read the scenario, we are going to build a genetic pedigree (a family tree) with the information from the scenario above. There are a few “conventions” on drawing pedigrees: women are depicted as circles, men as squares. If individuals are affected by a conditions, their circle/square gets filled in. When two individuals have children, they are linked by a line, with their children located below the line, all connected. As such, you can see generations forming in the pedigree, from oldest at the top to youngest at the bottom. An example pedigree is provided here for a hypothetical family, with all the kids and grandkids that resulted from one couple:

Now that we’ve seen how pedigrees are built, build your pedigree for the scenario that includes:

Emma Jacob’s mother Jacob Jacob’s father Matthew Emma’s deceased aunts Samuel Jacob’s deceased uncle Emma’s mother Emma’s father

C. Using the letter M for normal metabolism and m for msud, fill in the genotypes on your family tree for as many individuals as you can. If you know one allele, but not the other, use a dash in place of the unknown allele, e.g. M_ Now that you’re done, answer the following questions:

Lab 9: Follow the instructions and complete the assignment below. Submit your answers through the Lab 9 submission on Blackboard.

Lab 9 3

1. What are the phenotypes of Emma and Jacob for our gene of interest? What are their genotypes? 2. How could Emma and Jacob’s son have inherited msud even though neither parent suffers from msud? 3. Using the pedigree you drew from this scenario, how many individuals have had msud in this family? How many were most likely carriers? Justify your answers by explaining the logic of your pedigree. 4. What is the probability that Emma and Jacob’s next child would have msud? Justify your answer. If you were Emma and Jacob, now that you know the probability, would you have another child? Explain your answer briefly 5. Did you enjoy this exercise? Why or why not? Compare it to the 2 other exercises you did in Lab 8: is there one exercise that helped your learning on inheritance more than another? Explain briefly.

EXERCISE 2:

This activity can only be completed in pairs – your pair member can be anybody you’d like (your roommate, coworker, best friend, sibling over the phone, etc). A. Determine your personal genetic profile: work with one partner and determine your phenotype based on the characters illustrated in the figures (provided at the end of this homework). Determine the genetic basis of the phenotype when possible—for example, if you have blue eyes, then you know that the genotype for that phenotype is recessive (2 recessive alleles). If you have brown eyes, then you can only know for sure that you have 1 allele for brown eyes—the other allele could be for either brown or blue eye color. Fill out Table 1 (located at the end of this homework). To avoid confusions, I’ve completed the first few lines of that table for myself and my husband as an example to show you what it should look like…