You are a doctor examining a patient whose thymus never developed because of a medical condition called DiGeorge syndrome. You know that this usually results from the deletion of part of chromosome 22. The karyotype of this patient shows one copy of chromosome 22 that is of normal length; the second copy is shortened. This indicates that the genotype of this patient is _____ and that the expression of this trait is _____.

Question

Quizplus · Accepted Answer

The patient has a shortened copy of chromosome 22, indicating a deletion in that region. Since they have one normal copy and one shortened copy, they are heterozygous for the deletion. The fact that they have DiGeorge syndrome (a recessive condition) despite having only one shortened copy indicates that the expression of the trait is dominant. Therefore, the genotype is heterozygous and the expression is dominant.

You Are a Doctor Examining a Patient Whose Thymus Never