Fall 1999 Biology 111 Exam #2.5 - Molecular Genetics Half Exam

There is no time limit on this test, though I have tried to design one that you should be able to complete within 1.5 hours, except for typing. You are not allowed to use your notes, old tests, any electronic sources, any books, nor are you allowed to discuss the test with anyone until all exams are turned in by class on Monday November 1. EXAMS ARE DUE AT CLASS TIME ON MONDAY NOVEMBER 1. You may use a calculator and/or ruler. The answers to the questions must be typed on a separate sheet of paper unless the question specifically says to write the answer in the space provided. If you do not write your answers on the appropriate pages, I may not find them unless you have indicated where the answers are. There are 3 pages to this exam, including this cover sheet.


Please do not write or type your name on any page other than this cover page. Staple all your pages (INCLUDING THE TEST PAGES) together when finished with the exam.

Name (please print):


Write out the full pledge and sign:

Here is the honor code

"On my honor I have neither given nor received unauthorized information regarding this work, I have followed and will continue to observe all regulations regarding it, and I am unaware of any violation of the Honor Code by others."

How long did this exam take you to complete (excluding typing)?

3 pts.
1) Explain to me what a RFLP is and what the acronym stands for.
RFLP stands for Restriction Fragment Length Polymorphism. This is banding pattern that varies among different people. An RFLP is generated when the DNA from different individuals is digested with a restriction enzyme, electrophoresed, denatured, blotted, and probed. The different banding patterns indicate that each individual inherited a different DNA sequence so that the restriction fragments that contain the marker sequence are of different lengths.

This is not the figure that was printed but might be useful for studying....

8 pts.
2) The RFLP used here is linked to the disease gene and is located 3.5 map units away.
a) Which band is associated with the disease allele?
The upper band.
b) Is this a dominant, recessive or codominant disease? How do you know?
It is dominant and you can tell because the heterozygotes have the disease while the homozygotes do not have the disease. It only takes one mutant allele for the individuals to get the disease.
c) What should you tell the expectant parents of the fetus labeled with a "?"? Be as specific as you can.
There is a 50% chance of this fetus inheriting the disease.
With the modified figure, you should say that there is a 96.5% chance that this fetus will develop the disease. Since the upper band came from the mother, there is a 3.5% chance that the futus inherited the upper band but the wt allele. The father has only wt alleles and lower bands.

6 pts.
3) Construct a linkage map with these data that concern a disease locus and two RFLPs.

Answer ->

6 pts.
4) What components of DNA replication are used in DNA sequencing reactions and what components of sequencing reactions are unique to the sequencing reaction? You do NOT need to list components used in replication that are not used in sequencing.
.Shared components:
DNA polymerase, dNTPs, primer, template
Unique components:
ddNTPs, DNA primer,

8 pts.
5) Create a restriction map from these data generated with the two restriction enzymes, S and R. Draw the map on your typed pages.

Either map is a correct answer ->

5 pts.
6) Describe the genetic cause for most cases of cystic fibrosis. Be sure to include why this is a recessive disease at the molecular level.
The genetic cause for CF in 70% of all cases is a codon deletion that leads to a mutant protein that lack one amino acid (F508). This deletion mutation leads to the protein getting stuck in the ER and not reaching the PM. The protein is a Cl- ion channel and therefore Cl- ions do not leave the cell and enter the mucus so water is not drawn into the mucas and thus the mucus is too thick to be coughed up.
This is a recessive disease because the protein is non-functional so both alleles have to be affected in order for the person to lack any Cl- ion channels in their PM's.

6 pts.
7) a) Explain the molecular reason why Huntington's Disease is a dominant disease.
HD is dominant because the protein is hyperactive. It has too many glutamines in a row which causes it to stick to HAP-1 too long. As this adhesion accumulates over time, a person develops the disease. One bad allele is enough to cause a mutant form of huntingtin to start sticking too much to HAP-1 and the accumulation begins.
b) Could HD be treated with gene therapy the same way that CF can be treated?
No, because dominant diseases cannot be treated with another wild-type allele. The afflicted person already has one wt allele but it is useless in stopping the progression of the disease and a second wt allele will also be ineffective.

8 pts.
8) Tell me the genotypes and phenotypes of all F2 children in this family that has a sex-linked disease caused by a metabolic disorder. Note that shading has been omitted from the F2 generation so to receive full credit, you MUST fill in the appropriate shapes that HAVE TO BE shaded but do not fill in any shapes if you are not SURE that the child would have the disease. Do any shading on this page only.
Mom (#4) is a carrier and therefore she has a 50% chance of passing this mutation on to all four of her children. Therefore, we cannot be SURE if either of the boys will have the disease. The girls will either be carriers or not have any diseased alleles. Therefore, none of the symbols can be filled in with certainty.

m = mutation
+ = wt allele
? = either allele
Y = Y chromosome

5 = ? Y either diseased or wt
6 = ? Y either diseased or wt
7 = + ? wt phenotype
8 = + ? wt phenotype