Ans. C: Cystic fibrosis X-linked diseases usually occur in males. Males have only one X chromosome. A single recessive gene on that X chromosome will cause the disease. The Y chromosome is the other half of the XY gene pair in the male. However, the Y chromosome doesn't contain most of the genes of the X chromosome. It therefore doesn't protect the male. This is seen in diseases such as hemophilia and Duchenne muscular dystrophy. Autosomal dominant: Examples of this type of disorder are Huntington's disease, Neurofibromatosis 1, Marfan Syndrome, Hereditary nonpolyposis colorectal cancer, and Hereditary multiple exostoses, which is a highly penetrant autosomal dominant disorder. Autosomal recessive Examples of this type of disorder are cystic fibrosis, sickle-cell disease, Tay-Sachs disease, Niemann-Pick disease, spinal muscular atrophy etc. 3X-linked dominant X-linked hvpophosphatemic rickets, Rett syndrome, Incontinentia Pigmenti type 2 and Aicardi Syndrome X-linked recessive X-linked recessive conditions include the serious diseases Hemophilia A, Duchenne muscular dystrophy, G-6-PD deficiency and Lesch-Nyhan syndrome as well as common and less serious conditions such as male pattern baldness and red-green color blindness. Y-linked disorders Examples are Male Infeility and hyperichosis pinnae.