In humans there is a disease called Phenylketonuria (PKU)which is caused by a re
ID: 220417 • Letter: I
Question
In humans there is a disease called Phenylketonuria (PKU)which is caused by a recessive allele. People with this allele have a defective enzyme and cannot break down the amino acid phenylalanine. This disease can result in mental retardation or death. Let “E” represent the normal enzyme. Also in humans in a condition called galactose intolerance or galactosemia, which is also caused by a recessive allele. Let “G” represent the normal allele for galactose digestion. In both diseases, normal dominates over recessive. If two adults were heterozygous for both traits (EeGg), what are the chances of having a child that is completely normal? Has just PKU? Has just galactosemia? Has both diseases?
Explanation / Answer
Answer:
E= Normal for PKU ; e = PKU disease
G = Normal for galactosemia ; g = Galactosemia
EeGg x EeGg ------Parents
Ee x Ee = E_ (3/4) & ee (1/4)
Gg x Gg = G_ (3/4) & gg (1/4)
A child that is completely normal = E_G_ = ¾ * ¾ = 9/16
A child that has just PKU = eeG_ = ¼ * ¾ = 3/16
A child that has just galactosemia = E_gg = ¾ * ¼ = 3/16
A child that has both the diseases = eegg = ¼ * ¼ = 1/16