The following is a pedigree that shows the inheritance of a rare completely pene
ID: 253417 • Letter: T
Question
The following is a pedigree that shows the inheritance of a rare completely penetrant autosomal dominant disorder. DNA samples from generations I, II, III and IV were obtained and subjected to RFLP analysis. The results of the analysis are shown below. The RFLP marker used for the top panel is marker #135, and the one used for the bottom panel is marker #219, both in chromosome 17.
a. Can you determine if the gene causing the disorder is on chromosome 17? Explain in detail your conclusions.
b. Can you estimate the distance between the locus of the gene causing the disease and any of the RFLP markers? If you can, determine this distance.
c. If individuals III-4 and III-5 decide to have one more child, what are the odds that this child would have the disorder, just based on the genotypes of the parents and the inheritance pattern of the disorder?
d. Could you use RFLP analysis with the markers shown above to help determine the probability that the child will have the disorder? Which RFLP marker would you choose to analyze the DNA from the fetus for prenatal screening? How would you determine the odds of the child having the disease based on the RFLP results? Explain in detail.
-11-2 11-1 11-2 11-3 11-4 III-1 lI-2 IlI-3 111-4 IlI-5 1lI-6 II-7 IlI-8 1II-9 IV-1 IV-2 IV-3 IV-4 IV-5 IV-6Explanation / Answer
a) Yes we can determine that the autosomal dominant gene which is causing the disease is present on chromosome number 17 by looking DNA samples. By looking at the pattern of migration of DNA fragments on gel electrophoresis we can easily observe that the RFLp markers are similar in affected individuals which are carrying the two different markers.
b) No we cannot determine the distance between the two RFLP markers on the gene by simply looking at the migration of DNA fragments on gel electophoresis. This is so because no ladder has been run on the gel to determine it's size or length through which we can determine the gene distance.
c) The probability of the child of III - 4 and III-5 to be affected by the disease is only 50% . This is so because by looking at the pedigree chart we are able to interpret that III-4 is heterozygous for the autosomal dominant trait.
d) Yes we use RFLP markers to determine the probability of the child to have the disorder. I would choose both the RFLP markers for the prenatal screening purpose.
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