Nokea
Turner syndrome is suspected in an adolescent girl with short stature. What causes this?
- A. Absence of one of the X chromosomes
- B. Presence of an incomplete Y chromosome
- C. Precocious puberty in an otherwise healthy child
- D. Excess production of both androgens and estrogens
Correct Answer: A
Rationale: Turner syndrome is caused by an absence of one of the X chromosomes. Most girls who have this disorder have one X chromosome missing from all cells. No Y chromosome is present in individuals with Turner syndrome. These young women have 45 rather than 46 chromosomes.
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A father with an X-linked recessive disorder asks the nurse what the probability is that his sons will have the disorder. Which response should the nurse make?
- A. Male children will be carriers.
- B. All male children will be affected.
- C. None of the sons will have the disorder.
- D. It cannot be determined without more data.
Correct Answer: C
Rationale: When a male has an X-linked recessive disorder, he has one copy of the allele on his X chromosome. The father passes only his Y chromosome (not the X chromosome) to his sons. Therefore, none of his sons will have the X-linked recessive gene. They will not be carriers or be affected by the disorder. No additional data are needed to answer this question.
The inheritance of which is X-linked recessive?
- A. Hemophilia A
- B. Marfan syndrome
- C. Neurofibromatosis
- D. Fragile X syndrome
Correct Answer: A
Rationale: Hemophilia A is inherited as an X-linked recessive trait. Marfan syndrome and neurofibromatosis are inherited as autosomal dominant disorders. Fragile X is inherited as an X-linked trait.
Chromosome analysis of the fetus is usually accomplished through the testing of which?
- A. Fetal serum
- B. Maternal urine
- C. Amniotic fluid
- D. Maternal serum
Correct Answer: C
Rationale: Amniocentesis is the most common method to retrieve fetal cells for chromosome analysis. Viable fetal cells are sloughed off into the amniotic fluid, and when a sample is taken, they can be cultured and analyzed. It is difficult to obtain a sample of the fetal blood. It is a high-risk situation for the fetus. Fetal cells are not present in the maternal urine or blood.
Parents ask the nurse about the characteristics of autosomal dominant inheritance. Which statement is characteristic of autosomal dominant inheritance?
- A. Females are affected with greater frequency than males.
- B. Unaffected children of affected individuals will have affected children.
- C. Each child of a heterozygous affected parent has a 50% chance of being affected.
- D. Any child of two unaffected heterozygous parents has a 25% chance of being affected.
Correct Answer: C
Rationale: In autosomal dominant inheritance, only one copy of the mutant gene is necessary to cause the disorder. When a parent is affected, there is a 50% chance that the chromosome with the gene for the disorder will be contributed to each pregnancy. Males and females are equally affected. The disorder does not skip a generation. If the child is not affected, then most likely he or she is not a carrier of the gene for the disorder. In autosomal recessive inheritance, any child of two unaffected heterozygous parents has a 25% chance of being affected.
Parents ask the nurse about the characteristics of autosomal recessive inheritance. Which is characteristic of autosomal recessive inheritance?
- A. Affected individuals have unaffected parents.
- B. Affected individuals have one affected parent.
- C. Affected parents have a 50% chance of having an affected child.
- D. Affected parents will have unaffected children.
Correct Answer: A
Rationale: Parents who are carriers of a recessive gene are asymptomatic. For a child to be affected, both parents must have a copy of the gene, which is passed to the child. Both parents are asymptomatic but can have affected children. In autosomal recessive inheritance, there is a 25% chance that each pregnancy will result in an affected child. In autosomal dominant inheritance, affected parents can have unaffected children.