Question

12. Kevin is a male (XY) very short due to a condition known as de novo X-linked achondroplasia, which was caused by a denovo germline mutation in an X-linked gene. Did that mutation occur during spermatogenesis or oogenesis? (2 points) Do we expect that Kevin's daughter (XX) has achondroplasia - definitely, possibly or definitely not? Why? (2 points) 13. Consider the following pedigree: 167 8 9 10 Is this pedigree consistent with gray representing an autosomal recessive trait? If not, why not? (3 points) Is this pedigree consistent with gray representing an autosomal dominant trait? If not, why not? (3 points) 14. In humans, very few tumor supressor genes undergo genomic imprinting (that is, are expressed from only one allele). Why do you think that might be the case? (4 points)

Answer 1

12. Kevin who is a male (XY) has de novo X linked achondroplasia which causes him to be shorter than the usual height.

The disease is caused by a single nucleotide mutation in the FGFR3 gene which is responsible for converting cartilage to bones. The full name of the gene is fibroblast growth factor receptor 3. Thus achondroplasia can be termed as a skeletal disorder. Research has proved that the mutation of achondroplasia is associated with spermatogenesis.

Kevin's daughter who is a female(XX) also has equal chances of developing achondroplasia because it is an X linked dominant disease. The disease is very well known for causing dwarfism amongst children whose parents are prone to it as it is genetic in nature.

13. The pedigree analysis shows us a total of 3 generations. From the diagram, we can analyze that the disease is autosomal dominant in nature because the 1st generation ie the parents possess the disease. Thus, it is passed on to the offsprings. Therefore, a single copy of the defective gene in the primary generation is responsible for causing the disease in the next generations.

14. Tumor suppressor genes are the ones that slow down the continuous division of cells which ultimately lead to cancer formation. Genomic imprinting is a field of epigenetics which is caused due to methylation. However in the case of tumor suppressor genes, if methylation occurs the whole process gets inactivated. In the presence of inactivation of the suppressor genes, cancerous growth occurs. The methylation process of the suppressor genes has been studied in details and the two processes are the stochastic process and the intrusive process. The stochastic process is said to be a random event but the intrusive process is specific in nature. The methylation in both the cases are carried out by DNA methylase.