Faulty Tooth Enamel Formation
Amelogenesis imperfecta (AI) is a disorder of faulty tooth enamel formation. It is inherited in an autosomal dominant and X-linked dominant pattern.
The expression of AI disorder is determined by mutations in an autosomal gene. One copy of the mutated allele (A) will cause the disorder. Thus the expression of AI disorder is inherited in an autosomal dominant pattern.
In individuals that have the autosomal dominant allele the severity of the disorder is determined by mutations in a gene carried on the X chromosome. The non-severe abnormality (XN) is dominant over the severe (Xn) allele. In the absence of the autosomal dominant allele, the abnormality gene on the X chromosome is not expressed.
Question:
A woman with normal teeth had four children with a man with non-severe form of AI:
A boy was born without amelogenesis imperfecta
A girl was born without amelogenesis imperfecta
A boy was born with severe amelogenesis imperfecta
A boy was born with non severe amelogenesis imperfecta
Identify the parental genotypes. (1 mark)
Complete the Punnett square for the parental cross, and identify the possible phenotype ratios of the children. (2 marks)
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