1. In a woman with a 47,XXX karyotype, what types of gametes would theoretically be formed and in what proportions? What are the theoretical karyotypes and phenotypes of her progeny? What are the actual karyotypes and phenotypes of her progeny?

2. Individuals carrying a copy of the inv(9) described in the text are clinically normal. Provide two possible explanations.

3. The birth incidence rates of 47,XXY and 47,XYY males are approximately equal. Is this what you would expect on the basis of the possible origins of the two abnormal karyotypes? Explain.

4. How can a person with an XX karyotype differentiate as a phenotypically normal male?

5. A small centric ring X chromosome that lacks the X inactivation center is observed in a patient with short stature, gonadal dysgenesis, and intellectual disability. Because intellectual disability is not a typical feature of Turner syndrome, explain the presence of mental retardation with or without other associated physical anomalies in individuals with a 46,X,r(X) karyotype. In a prenatal diagnosis involving a different family, a somewhat larger ring that contains the X inactivation center is detected. What phenotype would you predict for the fetus in this pregnancy?

6. A baby girl with ambiguous genitalia is found to have 21-hydroxylase deficiency of the salt-wasting type. What karyotype would you expect to find? What is the disorder? What genetic counseling would you offer to the parents?

7. What are the expected clinical consequences of the following deletions? If the same amount of DNA is deleted in each case, why might the severity of each be different?

a. 46,XX,del(13)(pter→p11.1:)

b. 46,XY,del(Y)(pter→q12:)

c. 46,XX,del(5)(p15)

d. 46,XX,del(X)(q23q26)

8. Provide possible explanations for the fact that persons with X chromosome aneuploidy are clinically not completely normal.

9. In genetics clinic, you are counseling five pregnant women who inquire about their risk for having a Down syndrome fetus. What are their risks and why?

a. a 23-year-old mother of a previous trisomy 21 child

b. a 41-year-old mother of a previous trisomy 21 child

c. a 27-year-old woman whose niece has Down syndrome

d. a carrier of a 14;21 Robertsonian translocation

e. a woman whose husband is a carrier of a 14;21 Robertsonian translocation

10. A young girl with Down syndrome is karyotyped and found to carry a 21q21q translocation. With use of standard cytogenetic nomenclature, what is her karyotype?

11. Paracentric inversions generally do not raise the problem of imbalance in offspring. Why not?