Phenylketonuria (PKU) is a rare inherited metabolic disorder in humans. The allele for PKU is recessive.
a.[1]
Which of the following describes a homozygous genotype?
- Having two of the same alleles for a particular gene
- Having two different alleles for a particular gene
- Having only one allele for a gene located on a sex chromosome
b.[1]
Figure 1 shows the inheritance of PKU in one family.
The symbol of a shaded square is not in the key for Figure 1. What would this symbol represent?
c.
[3]
Parents 1 and 2 in Figure 1 have a child with PKU and some children without PKU. Complete the genetic diagram to show the possible genotypes of the children. Use the following symbols:
- PPP = allele for normal enzyme production (dominant)
- ppp = allele for PKU (recessive)
| Person 2: PPP | Person 2: ppp | |
|---|---|---|
| Person 1: PPP | Box (i) | PpPpPp |
| Person 1: ppp | Box (ii) | Box (iii) |
Identify the genotypes for:
- Box (i)
- Box (ii)
- Box (iii)
d.[1]
What is the phenotype of a person with the genotype PpPpPp?
e.[1]
What percentage of the offspring shown in the genetic diagram will have PKU?