Tracing the path of an autosomal dominant trait Trait neurof

Tracing the path of an autosomal dominant trait Trait: neurofibromatosis Forms of the trait: The dominant form is neurofibromatosis, caused by the production of an abnormal form of the protein neurofibromin. Affected individuals show spots of abnormal skin pigmentation and non-cancerous tumors that can interfere with the nervous system and cause blindness. Some tumors can convert to a cancerous form. The recessive form is a normal protein - in other words, no neurofibromatosis. A typical pedigree for a family that carries neurofibromatosis is shown below. Note that carriers are not indicated with half-colored shapes in this chart. Use the letter \"N\" to indicate the dominant neurofibromatosis allele, and letter \"n\" for the normal allele. Analysis Questions: Is individual #1 most likely homozygous? Explain how you can tell. What is the genotype of individual #3? Can you be sure of the genotypes of the affected siblings of individual #3? Explain.

Solution

Please find the answers below:

Part 1: It can be seen from the pedigree that the female offspring of the couple or parents is affected from the disease. Also, it should be noted that some females and male offsprings are affected but some are not. This clearly suggests that the father is not a carrier of this allele because if he was a carrier, the chances of transmission of this allele from the father will be 100% in all the females since the father always transfers an X chromosome to daughter. Further, the observation that only some of male and female offsprings are affected, it can be concluded that the inidividual 1 or the mother is a carrier or heterozygous in nature.

Part 2: It can be seen from the pedigree that the mother is heterozygous and father is not a carrier. This means that the individual 2 who itself is affected and his wife both are affected by the disease. Further, it should be noted that the wife of individual 2 is heterozygous in nature. Thus, the genotype of the individual 3 will be either Nn or NN in nature. In both conditions, he will be affected by the disease.

Part 3: As for the siblings of individual 3, it can be concluded that all of them must be affected by the disease. This is because their mother is a heterozygous carrier and expresses the disease whereas the father is also affected. Thus, the father will always transfer a diseased allele to his offsprings. Further, since the disease is autosomal dominant in nature and provided the information that the father and mother both are heterozygous in nature, it is very likely that some offsprings will not be affected because they will be carrying the homozyogous recessive alleles.