Use the information in the pedigree and the information in the southern blot of

Question

Use the information in the pedigree and the information in the southern blot of the RFLPs of the gene associated with a rare autosomal disease to answer the following questions. Individuals affected by the disease are coded black. Assume penetrance for the disease genotype is 25%.

A. Based on the information in the description, pedigree, and blot what is the most likely mode of inheritance of the disease. Briefly explain your reasoning.

B. Which band in the gel is associated with the disease? In other words, which band represents the allele that causes the disease? (band closest to the wells (longest DNA strand) or band farthest away from the wells (shortest strand of DNA))

C. What is the probability that II-4 is affected?

D. What is the probability that III-3 will be affected?

E. If II-4 and II-5 had 4 children total, what is the probability that 2 would be affected and 2 would be unaffected?

F. Provide an explanation for what may cause less than 100% penetrance? (in your answer define penetrance)

Explanation / Answer

A. From the RFLP gel blot: The disease gene is found in male of generation l but not expressed phenotypically, similarly it is found in generation lll but not seen phenotypically, it is seen and expressed in generation lll. So clearly there is skipping of generation by the disease gene which is a feature of AUTOSOMAL RECESSIVE INHERITANCE PATTERNS.

B. In the pedigree we can clearly see that a male of generation lll is affected and it's corresponding Band farthest from the wells is representing the disease gene, and similar is the case for band 1 of generation l and band 4 of generation lll.

C. The affected and carrier individuals in generation two :

The carrier patients of generation l will have a heterozygous genotype of Yg and Yg and the offsprings will be YY, Yg, Yg, GG and the phenotype will be healthy, 2 carriers and 1 affected. From pedigree it is clear that ll-2 is the one affected with recessive genes 'gg' while the ll-3 is unaffected 'YY'(justified by no band in RFLP blot) and the ll-4 is having 50% probability to be a carrier and zero for being affected; as we can see the disease gene band on blot but is not assertively expressed like ll-2.

D. The parents of lll-3 are ll-4 and Il-5. Here from blot we can say that ll-4 is a carrier and ll-5 is healthy/ unaffected so there is no chance(0,%) of generation of affected lll-3. This is possible only if both the parents are carriers of the disease gene but here only one parent ll-4 is carrier and other parent ll-5 does not have the disease gene at all.

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