Question

A rare form of dwarfism that also included hearing loss was found to run in a particular family. It is inherited as a dominant trait. It was discovered that an affected individual had one normal copy of chromosome 15 and one abnormal copy of chromosome 15 that was unusually long. How would you determine if the unusually long chromosome 15 was causing this disorder?

Answer 1

The given data is that chromosome 15 is abnormally long in the affected individual. The trait is dominant, which means that just one abnormal copy is enough to determine the phenotype. In order to verify this, a conventional karyotyping can be done for affected vs normal individuals. Normal individuals would give a single banding pattern for chromosome 15. The abnormal individuals will give two patterns upon karyotyping for chromosome 15. The long chromosome can arise most probably via duplication of a part of the chromosome since the trait is dominant. The duplication can be detected by a variant of Fluorescence in situ hybridization (FISH) called comparative genomic hybridization (CGH). The genomic imbalance and the duplicated genes can be found. The genes that are duplicated can then be studied either using known knowledge, genetic screens or bioinformatics to test for the phenotypes of dwarfism and hearing loss.