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Chapter 6: Genetic and Developmental Disorders Test Bank
1. Characteristics of X-linked (sex-linked) recessive disorders include
a. all daughters of affected fathers being carriers.
b. boys and girls being equally affected.
c. the son of a carrier females having a 25% chance of being affected.
d. affected fathers transmitting the gene to all their sons.
All daughters of affected fathers are carriers. X-linked (sex-linked) disorders affect primarily males. A carrier femalehas a 1 in 2 chance of producing an affected son. Affected fathers transmit the defective gene to none of their sons but to all their daughters.
REF: Pg. 103
2. A fetus is most vulnerable to environmental teratogens during a. birth.
c. the first trimester. d. the last trimester.
Between the third and ninth week of gestation, the embryo is very vulnerable to teratogenesis, with the fourth and fifth weeks being the time of peak susceptibility. By birth, fetal development is complete and not vulnerable to environmental teratogens. Prior to the third week of gestation, either exposure to a teratogen generally damages so few cells that the embryo develops normally, or spontaneous abortion occurs due to major cell damage. Fetal insults occurring after the third month are more likely to result in growth retardation or injury to normally formed organs.
REF: Pg. 108
3. Results of biochemical tests indicate an infant has phenylketonuria (PKU). The parents ask what PKU means. Correct responses would include all the following except PKU
a. is an enzyme deficiency resulting in the inability to metabolize phenylalanine.
b. is an inborn error of metabolism.
c. results from a chromosome abnormality called nondisjunction.
d. is transmitted as an autosomal recessive disorder.
PKU is not a chromosome abnormality, but instead a single-gene abnormality often referred to asinborn errors of metabolism. The other answer choices are true statements regarding PKU.
REF: Pgs. 100-103
4. The parents of a child with PKU are concerned about the risk of transmitting the disorder in future pregnancies. The correct assessment of the risk is
a. each child has a 25% chance of being a carrier.
b. each child has a 25% chance of being affected.
c. since one child is already affected, the next three children will be unaffected.
d. one cannot predict the risk for future pregnancies.
As an autosomal recessive disorder, the mating of two carriers (heterozygous) results in a 1 in 4 chance of producing anaffected offspring and a 2 in 4 chance of producing an offspring who carries the disease. The mating of two carriers (heterozygous) results in a 2 in 4 chance of producing an offspring who carries the disease. The mating of two carriers (heterozygous) results ina 1 in 4 chance of producing an affected offspring and a 2 in 4 chance of producing an offspring who carries the disease. One canpredict the risk of future pregnancies.
REF: Pgs. 101-103
5. Information parents should be given about the consequences of PKU includes
a. high dietary phenylalanine may help induce enzyme production.
b. PKU is commonly associated with other congenital anomalies.
c. failure to avoid phenylalanine results in progressive mental retardation.
d. mental retardation is inevitable.
Failure to avoid phenylalanine results in progressive mental retardation. Phenylketonuria (PKU) results from an inability to metabolize the amino acid phenylalanine due to lack of the enzyme phenylalanine hydroxylase. Intake of phenylalanine wil not help induce enzyme production. This disorder is not necessarily associated with other congenital anomalies. Mental retardation can be prevented or lessened with avoidance of phenylalanine.
REF: Pg. 103
Copyright 2013, 2010, 2005 Saunders, an imprint of Elsevier Inc. All rights reserved. 1
6. Children with PKU must avoid phenylalanine in the diet. Phenylalanine is most likely to be a component of a. fat.
Phenylalanine is an amino acid found in protein. Most fats, sugars, and carbohydrates do not contain phenylalanine.
REF: Pg. 103
7. A point mutation
a. results from the addition or loss of one or more bases.
b. is due to the translocation of a chromosomal segment.
c. always produces significant dysfunction.
d. involves the substitution of a single base pair.
A point mutation involves a single base pair substitution. A point mutation does not result from the addition or loss of bases, or from translocation of a chromosomal segment, but rather from a substitution. The inclusion of the abnormal amino acid in the sequence of the protein due to a point mutation may or may not be of clinical significance.
REF: Pg. 95
8. Males are more likely than females to be affected by ________ disorders.
d. chromosomal nondisjunction
Males are more likely than females to be affected by X-linked disorders. Females express the X-linked disease only in the rare instance in which both X chromosomes carry the defective gene. Males, however, do not have the safety margin of two X chromosomes and express the disease if their one and only X chromosome is abnormal. Males and females are equally affected by autosomal-dominant and autosomal-recessive disorders. Chromosomal nondisjunction means that paired homologous chromosomes fail to separate normally during either the first or second meiotic division, resulting in germ cells that have an abnormal number of chromosomes. This can occur in both males and females equally.
REF: Pg. 103
9. The primary factor associated with risk of Down syndrome is
a. family history of heritable diseases.
b. exposure to TORCH syndrome organisms.
c. maternal alcohol intake.
d. maternal age.
Advanced maternal age is associated with Down syndrome in the most common form of the disease. A family history of heritable disease is not the primary factor and occurs in only 4% of cases. Exposure to TORCH syndrome organisms is not a risk factor for Down syndrome. Maternal alcohol intake is not a risk factor for Down syndrome.
REF: Pgs. 98-99
10. Cystic fibrosis is a single gene disorder that primarily affects
a. brain and heart.
b. kidney and adrenals.
c. lungs and pancreas.
d. liver and intestine.
The alteration in chloride transport associated with cystic fibrosis is associated with production of abnormally thick secretions in glandular tissues. The lung bronchioles and pancreatic ducts are primarily affected, often resulting in progressive destruction of these organs. The brain, heart, kidneys, and liver are not the primary organs affected with cystic fibrosis.
REF: Pg. 103
11. Huntington disease is often transferred to offspring before a parent knows of the genetic possibility of this disease, because
a. symptoms are so mild that they are not recognized.
b. symptoms often do not occur until approximately 40 years of age.
c. genetic testing for the disease is not possible.
d. the genetic alteration is rarely expressed.
Signs of mental deterioration and involuntary muscle movements do not appear until approximately age 40. The delayed onset means the parent may transmit the disorder to offspring before he or she knows they have the disorder. Symptoms of Huntingtons disease are not necessarily mild, and are not the reason for delayed identification of the genetic susceptibility. Genetic testing for the disease is possible. The genetic alteration is expressed if the triplet repeats are greater than 40.
REF: Pg. 101
Copyright 2013, 2010, 2005 Saunders, an imprint of Elsevier Inc. All rights reserved. 2
12. Huntington disease primarily affects the _____ system. a. neurologic
c. gastrointestinal d. endocrine
Huntington disease primarily affects the neurologic system and leads to uncontrolled movement of the extremities. Huntington disease does not primarily affect the muscles, although the altered neural involvement secondarily causes involuntary movement of the arms and legs. It also does not affect the gastrointestinal and endocrine systems.
REF: Pg. 101
13. The risk period for maternal rubella infection leading to congenital problems begins
a. prior to conception.
b. during the last trimester.
c. at birth.
d. all through pregnancy.
The risk period for maternal rubella infection begins prior to conception and extends to 20 weeks gestation, after which the virus rarely crosses the placenta. The virus rarely crosses the placenta after 20 weeks gestation. The virus does not cross the placenta at birth and would not cause congenital problems at this point. The risk period for maternal rubella infection begins prior to conception and extends to 20 weeks gestation, after which the virus rarely crosses the placenta.
REF: Pg. 109
14. Characteristics of Marfan syndrome include that it (Select all that apply)
a. is a single-gene disorder.
b. involves alterations in connective tissue.
c. leads to skeletal and joint deformities.
d. leads to short stocky build.
e. results in dangerous cardiovascular disorders.
ANS: A, B, C, E
Marfan syndrome is a single-gene disorder that involves alterations in connective tissue and leads to skeletal and joint deformities. The aorta weakens and may rupture and cardiac valves may malfunction. Individuals with Marfan syndrome are typically tal and slender, with long, thin arms and legs, rather than short and stocky.
REF: Pgs. 100-101
Copyright 2013, 2010, 2005 Saunders, an imprint of Elsevier Inc. All rights reserved. 3
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