Single gene defect ca using multiple unrelated problems -

Ans. is 'a' i.e. Pleiotropy o Pleiotropy occurs when a mutation in a single gene produces effects on more than one characteristic, that is causes multiple mutant phenotypes. o In humans this phenomenon is most obvious when mutations in single genes causes diseases with seemingly unrelated symptoms. Some examles of this phenomenon are : Transcription factor TBx5 mutations that cause the cardiac and limb defects of Holt-Oram syndrome. Glycosylation enzyme MPI mutations that produce the severe mental retardation and blood coagulation abnormalities of type Ib congenital disorders of glycosylation. o DNA damage repair protein NBSI mutations that lead to microcephaly, immunodeficiency and cancer predisposition in Nijmegen breakage syndrome.