Exam 6: Pedigree Analysis, Applications, and Genetic Testing

The pedigree below shows a rare autosomal recessive trait segregating. What is the probability of the first child of a marriage between III-3 and III-7 being affected?

If monozygotic and dizygotic twins have the same concordance value for a trait, which of the following is TRUE?

Could the characteristics followed in the pedigree be caused by an X-linked recessive allele?

Which of the following conditions is MOST commonly screened for in maternal blood tests?

Heterozygote screening normally involves:

A maternal blood screening test carried out in the second month of a pregnancy indicates a level of $\alpha$ -fetoprotein that is significantly higher than normal. a. What is $\alpha$ -fetoprotein? b. What does a higher than normal level of $\alpha$ -fetoprotein in the mother's blood indicate? c. Critique the maternal blood screening test-specifically, what are its limitations? d. Given the limitations of the tests, why are they so commonly ordered? e. If you were the doctor who ordered this test, how would you proceed?

Is it possible that the characteristic in the pedigree below could be X-linked dominant? If so, what is the genotype of each individual? If not, explain why not, giving specific genotypes. Use alleles B and b.

Explain what it means for a genetic counselor to use "nondirected counseling."

Suppose that a harmful autosomal recessive condition is found at a particularly high frequency within a certain population. Public health officials would like to reduce the incidence of the condition in the population using genetic testing and genetic counseling. Which of the following programs would be MOST appropriate and most effective in achieving the desired outcome?

In pedigree analysis, consanguinity refers to:

Is it possible that the characteristic in the pedigree below could be X-linked recessive? If so, what is the genotype of each individual? If not, explain why not, giving specific genotypes. Use alleles A and a.

What is the MOST likely mode of inheritance for the trait segregating in the pedigree below?

Is it possible that the characteristic in the pedigree below could be autosomal dominant? If so, what is the genotype of each individual? If not, explain why not, giving specific genotypes. Use alleles D and d.

Which of the following statements is NOT true concerning newborn screening?

Which of the following statements concerning chorionic villus sampling are TRUE? (Select all that apply.)

Both members of an expecting couple are carriers of Tay-Sachs disease, which is an autosomal recessive condition that causes deterioration of nervous function within several months after birth and usually death by age 4. The couple wants to avoid having a child with Tay-Sachs disease, and a DNA test is available to detect the mutant allele. It is early in the pregnancy, and the couple is willing to abort the fetus if it is homozygous for the allele that causes Tay-Sachs disease. However, the couple wishes to have the abortion performed as early as possible if one is to be done. Which would be the MOST appropriate test to determine the genotype of the fetus?

Assuming that it is not a Y-linked trait, suggest the MOST likely mode of inheritance for the rare trait shown in the pedigree below.

June has two brothers with Becker muscular dystrophy (BMD), an X-linked recessive condition that allows affected males to survive into adulthood. Her parents are phenotypically normal. She marries Sheldon who also has BMD. June and Sheldon have a daughter. What is the probability that this daughter will have BMD?

Most pedigrees showing the hypothetical human trait show the following characteristics: • Females are affected twice as frequently as males. • Affected fathers may have affected daughters but never affected sons. • Half the children of affected mothers and normal fathers are affected. What is the MOST likely mode of inheritance for this disorder?

Today, more than 1200 genetic tests are available to doctors and patients for use in diagnosis and treatment of health conditions, and more will become available in the near future. Genetic testing is becoming more common in medical practice, and genetic testing is expected to become commonplace. Explain the complications that are associated with genetic testing and why specialized genetic counselors are needed in medical practice.