Junctional epidermolysis bullosa (JEB) is a severe skin disorder that results in blisters over the

•5. Junctional epidermolysis bullosa (JEB) is a severe skin disorder that results in  blisters over the entire body.  The disorder is caused by an autosomal recessive mutation on chromosome 1. A case with a male newborn who was born with JEB and died at 2 months of age. The child had healthy unrelated parents.  Chromosomal analysis revealed that the infant had 46 normal –appearing chromosomes. Analysis of DNA showed his mother was heterozygous for the mutation and the father had 2 normal alleles.  Paternity testing confirmed the assumed father was the real father.

•a. Assuming no new mutations occurred in the family, explain the presence of an autosomal recessive disease in a child when the mother is heterozygous and the father is homozygous normal. (2pts)



•b. If the karyotype had been 47, 1+ , would the severity of the phenotype be any different? Explain. (2pts)