Lecture 2 PDF - Genetic Counselling

A woman comes to your office for genetic counselling because her niece has cystic fibrosis (autosomal recessive). She is concerned that she might be a CF carrier. What is the probability that this woman is a heterozygous carrier for a cystic fibrosis mutation? ½ What is the probability that the ch...

A woman comes to your office for genetic counselling because her niece has cystic fibrosis (autosomal recessive). She is concerned that she might be a CF carrier. What is the probability that this woman is a heterozygous carrier for a cystic fibrosis mutation? ½ What is the probability that the child (P) will be affected with Phenylketonuria PKU (autosomal recessive disorder), knowing that his/her mother is a known heterozygous carrier of a PKU mutation? What is the probability that the child (P) will be affected with Phenylketonuria PKU (autosomal recessive disorder), knowing that his/her mother is a known heterozygous carrier of a PKU mutation? 1 x R x ¼ = 1 x 1/64 x ¼ = 1/256 Phenylketonuria is a recessive inborn error of metabolism of the amino acid phenylalanine that results in severe mental retardation of affected children. The female II-3 (red circle) in the pedigree shown below is affected, whereas II-2 and II-4 are not affected. If the persons III-1 and III-2 mate, what is the probability that their offspring will be affected? (Assume that persons II-1 and II-5 are homozygous for the normal allele.) Phenylketonuria is a recessive inborn error of metabolism of the amino acid phenylalanine that results in severe mental retardation of affected children. The female II-3 (red circle) in the pedigree shown below is affected, whereas II-2 and II-4 are not affected. If the persons III-1 and III-2 mate, what is the probability that their offspring will be affected? (Assume that persons II-1 and II-5 are homozygous for the normal allele.) III-1 (heterozygous) x III-2 (heterozygous) x ¼ 1/3 x 1/3 x ¼ = 1/36  Pedigree Analysis How do you evaluate a pedigree to determine the mode of inheritance of a particular trait? - form a hypothesis as to how the trait is inherited - test the pedigree for consistency with that hypothesized mode of inheritance - if consistent with the hypothesized mode of inheritance, -accept your hypothesis only when all other modes of inheritance can be been ruled out.  P What is the probability that this pending pregnancy will be affected? What mode of inheritance? What mode of inheritance? Huntington disease: autosomal dominant late onset rare What is the probability that this child may get Huntington disease (assuming a long life)? Probability father has inherited the Huntington allele = 1/2 Probability child inherits Huntington allele from the father if the father inherited the Huntington allele = 1/2 Probability father has inherited the Huntington allele = 1/2 Probability child inherits Huntington allele from the father if the father inherited the Huntington allele = 1/2 1/2 x 1/2 = 1/4