Molly and Ryan are devastated to hear that boys with DMD are usually only health

Question

Molly and Ryan are devastated to hear that boys with DMD are usually only healthy until the age of 4 or 5, when their muscles began to weaken. This means Parker, age 5, will probably need a wheelchair in a few years and will likely die before the age of 25. The parents conduct further research and find that the mutation occurs in the dystrophin gene, which is the largest gene on the human X chromosome. It codes for the protein Dystophin: an important structural component within muscle tissue. This mutation results from a deletion of part of the gene and thus the DNA instructions for building the protein Dystophin are incomplete. After receiving a large amount of information concerning their son's health and realizing Molly must be a carrier for DMD, Molly and Ryan began to worry about their other children and the unborn child Molly carries. In light of this, they visit a genetic counseling center where the tests could be done to determine the genotype of each child. The genetic counselor takes a small sample of blood from each family member, and a fetal blood sample for the unborn baby to isolate the gene known to carry DMD from each individual. The samples the genetic counselor isolated are now in your hands. As a table group you will be determining which children have DMD, which are carriers of DMD, and which are free of the mutant DMD gene. You will use a tool called electrophoresis to simulate the procedure that the genetic counseling lab would also be using. Electrophoresis is a technique that separates DNA fragments by size using an electric current. Genetic counselors use this method to identify individuals' genotypes: this includes determining paternity. While you run your tests (they take about 30 minutes) you will be completing additional lab activities that will aid in your understanding of what a mutation is and how it affects the production of specific proteins. Before you prepare your gel, answer the following: 1. How would you write the genotype for DMD for the father, Ryan? What about for the mother, Molly? (Remember. DMD is a recessive mutation in the D/d gene, and this gene is located on X chromosomes) 2. How do we know that Ryan isn't a carrier? 3. Which children could have DMD? Explain how you determined this. 4. Which children could be carriers? 1: Electrophoresis Gel Gel electrophoresis is a method used to separate and analyze biomolecules, including DNA. It helps us compare biomolecule fragments, based on size and charge. Today we will focus on the size of DNA fragments from the DMD gene. Gel electrophoresis uses an electric current to pull DNA molecules through a thick gel-like substance called agarose. Small DNA fragments will move faster through the gel than large ones. Therefore, the DNA fragment that moves fastest and farthest through the dye will represent the mutant DMD allele, d (a deletion mutation, which is missing a section making it smaller than non mutant strands). The slower moving DNA fragment will represent the healthy, non-mutant D allele (which doesn't have the deletion and is therefore longer). Prior to getting your DNA samples, show each potential outcome by diagramming on Figure 2 whether one or two bands would be present and show relative distances traveled by each band Tips: Females have two X chromosomes and males only have one. The mutant DMD gene has a deletion and this gene is on the X chromosome Smaller fragments of DNA travel faster through the gel Two copies of the same allele will travel together, appearing as a single band.

Explanation / Answer

1. XY -Ryan(normal) ; XX- Carrier Molly

X Y

2.Males are not carriers as they have only one X chromosome and if that chromosome is affected he will subjected to the disease.

3.25 % of the male children will be normal and 25% will be the sufferer of the disease.

4.25% of girls would be normal and 25% would be carriers as shown by X.

X XX XY X XX XY

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