Consider the following pedigree, which traces the inheritance of a si.pdf
- 1. Consider the following pedigree, which traces the inheritance of a single-gene hereditary disease. Only individuals that are either affected or normal are shown. In other words, potential heterozygotes are NOT indicated. Characterize each of the following modes of inheritance as: impossible, unlikely, or probable. Justify your answers. Autosomal dominant Autosomal recessive X-linked dominant X-Iinked recessive Y linked Solution Single gene herediary diseases are mainly caused by a change of any one gene in a particular DNA.Its divided into diiferemt categories like dominant ,recessive and X linked.Square indicates a male and circle female.According to the diagram affected male is crossed with an unaffected female.The progeny obtained is affected daughters and unaffected sons. Autosomal dominant: in this case, the father — has a 50 percent chance of having an affected child with one mutated gene (dominant gene) and a 50 percent chance of having an unaffected child with two normal genes (recessive genes).But, in our case none of the sons are affected which means its criss cross inheritance that is from father to daughter.Hence , this case is unlikely Autosomal recessive:To have an autosomal recessive disorder, you inherit two mutated genes, one from each parent. These disorders are usually passed on by two carriers.The cross given in the question is not between the two carriers.The male parent is affected for sure hence this case is impossible X linked dominant:As in autosomal dominant inheritance, only one copy of a disease allele on the X chromosome is required for an individual to be susceptible to an X-linked dominant disease.Both males and females can be affected, although males may be more severely affected because they only carry one copy of genes found on the X chromosome. Some X-linked dominant disorders are lethal in males.When a female is affected, each pregnancy will have a one in two (50%) chance for the offspring to inherit the disease allele. When a male is affected, all his daughters will be affected, but none of his sons will be affected.So, there are probable chance for this type of inheritance X linked recessive:For X-linked recessive disorders, an affected father who has a mutation in a gene on the X chromosome can transmit either the X chromosome with this mutation or a Y chromosome to his children. If the mother is not affected or a carrier, none of his sons will be affected since they can only inherit a normal X chromosome from their mother and they inherit a Y chromosome from their father. Each daughter will have a 50% chance of being an unaffected carrier and a 50% chance of both X chromosomes being normal.In our cross all daughters are affected which means this type of inheritance is impossible
- 2. Y linked:This type of inheritance is impossible in this case as all female children are getting affected.If it would have been Y linked then only sons should have been affected as Y chromosome is present only in males.Hence this type of inheritance is impossible