Nokea
Which abnormality is a common sex chromosome defect?
- A. Down syndrome
- B. Turner syndrome
- C. Marfan syndrome
- D. Hemophilia
Correct Answer: B
Rationale: Turner syndrome is caused by an absence of one of the X chromosomes. Down syndrome is caused by trisomy 21 (three copies rather than two copies of chromosome 21). Marfan syndrome is a connective tissue disorder inherited in an autosomal dominant pattern. Hemophilia is a disorder of blood coagulation inherited in an X-linked recessive pattern.
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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.
A woman, age 43 years, is 6 weeks pregnant. It is important that she be informed of which?
- A. The need for a therapeutic abortion
- B. Increased risk for Down syndrome
- C. Increased risk for Turner syndrome
- D. The need for an immediate amniocentesis
Correct Answer: B
Rationale: Women who are older than age 35 years at the birth of a single child or 31 years at the birth of twins are advised to have prenatal diagnosis. The risk of having a child with Down syndrome increases with maternal age. There is no indication of a need for a therapeutic abortion at this stage. Turner syndrome is not associated with advanced maternal age. Amniocentesis cannot be done at a gestational age of 6 weeks.
Parents ask the nurse if there was something that should have been done during the pregnancy to prevent their childs cleft lip. Which statement should the nurse give as a response?
- A. This is a type of deformation and can sometimes be prevented.
- B. Studies show that taking folic acid during pregnancy can prevent this defect.
- C. This is a genetic disorder and has a 25% chance of happening with each pregnancy.
- D. The malformation occurs at approximately 5 weeks of gestation; there is no known way to prevent this.
Correct Answer: D
Rationale: Cleft lip, an example of a malformation, occurs at approximately 5 weeks of gestation when the developing embryo naturally has two clefts in the area. There is no known way to prevent this defect. Deformations are often caused by extrinsic mechanical forces on normally developing tissue. Club foot is an example of a deformation often caused by uterine constraint. Cleft lip is not a genetic disorder; the reasons for this occurring are still unknown. Taking folic acid during pregnancy can help to prevent neural tube disorders but not cleft lip defects.
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.
Which genetic term refers to a person who possesses one copy of an affected gene and one copy of an unaffected gene and is clinically unaffected?
- A. Allele
- B. Carrier
- C. Pedigree
- D. Multifactorial
Correct Answer: B
Rationale: An individual who is a carrier is asymptomatic but possesses a genetic alteration, either in the form of a gene or chromosome change. Alleles are alternative expressions of genes at a different locus. A pedigree is a diagram that describes family relationships, gender, disease, status, or other relevant information about a family. Multifactorial describes a complex interaction of both genetic and environmental factors that produce an effect on the individual.