Chapter 4: Genes and Genetic Diseases Flashcards
Transcription is best defined as a process by which:
a. DNA polymerase binds to the promoter site on ribonucleic acid (RNA).
b. RNA directs the synthesis of polypeptides for protein synthesis.
c. RNA is synthesized from a DNA template.
d. A base pair substitution results in a mutation of the amino acid sequence.
ANS: C
Transcription is the process by which RNA is synthesized from a DNA template. The
correct option is the only one that accurately defines the term transcription.
PTS: 1 REF: Page 141
The most clinically useful technique for prenatal diagnosis of chromosomal abnormalities at 3 months’ (12 weeks’) gestation is: a. Gene mapping c. Amniocentesis b. Linkage analysis d. Chorionic villus sampling
ANS: D
Chorionic villus sampling consists of extracting a small amount of villous tissue directly
from the chorion. This procedure can be performed at 10 weeks’ gestation and does not
require in vitro culturing of cells; sufficient numbers are directly available in the extracted
tissue. Thus the procedure allows prenatal diagnosis at approximately 3 months’ gestation
rather than at nearly 5 months’ gestation. The correct option is the only one that accurately
describes the most useful technique for prenatal diagnosis of chromosomal abnormalities.
PTS: 1 REF: Page 136 | Box 4-1
What syndrome, characterized by an absent homologous X chromosome with only a single
X chromosome, exhibits features that include a short stature, widely spaced nipples, and
webbed neck?
a. Down
c. Turner
b. Cri du chat
d. Klinefelter
ANS: C
What is the second most commonly recognized genetic cause of mental retardation?
a. Down syndrome
c. Klinefelter syndrome
b. Fragile X syndrome
d. Turner syndrome
ANS: B
The fragile X syndrome is the second most common genetic cause of mental retardation
(after Down syndrome). The correct option is not observed with enough frequency to be
recognized as the second most common cause of mental retardation.
PTS: 1 REF: Page 151
What is the blood type of a person who is heterozygous, having A and B alleles as codominant? a. A c. O b. B d. AB
ANS: D
People diagnosed with neurofibromatosis have varying degrees of the condition because of the genetic principle of: a. Penetrance c. Dominance b. Expressivity d. Recessiveness
ANS: B
Expressivity is the extent of variation in phenotype associated with a particular genotype.
If expressivity of a disease is variable, then the penetrance may be complete but the
severity of the disease can vary greatly. A well-known example of variable expressivity in
an autosomal dominant disease is type 1 neurofibromatosis. The correct option is the only
one that accurately describes the presence of varying degrees of symptomatologic
characteristics.
Which genetic disease has been linked to a mutation of the tumor-suppressor gene?
a. Hemochromatosis
c. Familial breast cancer
b. Retinoblastoma
d. Hemophilia A
ANS: B
Which is an important criterion for discerning autosomal recessive inheritance?
a. Consanguinity is sometimes present.
b. Females are affected more than males.
c. The disease is observed in both the parents, as well as in the siblings.
d. On average, one half of the offspring of the carrier will be affected
ANS: A
Consanguinity is often an important characteristic of pedigrees for recessive diseases;
relatives share a certain proportion of genes received from a common ancestor. The correct
option is the only one that accurately identifies a required factor in autosomal recessive
genetic inheritance.
PTS: 1 REF: Page 155
Males, having only one X chromosome (as is expected), are said to be:
a. Homozygous
c. Hemizygous
b. Heterozygous
d. Ambizygous
ANS: C
Males are more often affected by which type of genetic disease?
a. Sex-linked dominant
c. Sex-linked
b. Sex-influenced
d. Sex-linked recessive
ANS: D
Males are more frequently affected by X-linked recessive diseases, with the difference
becoming more pronounced as the disease becomes rarer. The correct option is the only
one that is a characteristic of a male-dominate disease.
PTS: 1 REF: Page 156
An X-linked recessive disease can skip generations because:
a. Females are hemizygous for the X chromosome.
b. The disease can be transmitted through female carriers.
c. Mothers cannot pass X-linked genes to their sons.
d. These diseases need only one copy of the gene in females.
ANS: B
Skipped generations are often observed in X-linked recessive disease pedigrees because
the gene can be transmitted through female carriers. Males are hemizygous for genes on
the X chromosome. Fathers cannot pass X-linked genes to their sons. X-linked recessive
diseases are observed significantly more often in males than in females, because males
need only one copy of the gene to express the disease.
PTS: 1 REF: Page 157
The presence of a zygote having one chromosome with the normal complement of genes
and one with a missing gene is characteristic of which genetic disorder?
a. Cri du chat
c. Klinefelter syndrome
b. Down syndrome
d. Turner syndrome
ANS: A
This description is only accurate for Cri du chat syndrome.
PTS: 1 REF: Pages 148-149
Examples of prenatal diagnostic studies include: (Select all that apply.)
a. Chorionic villus sampling (CVS)
b. Amniocentesis
c. Carrier screening
d. Preimplantation genetic diagnosis (PGD)
e. Drug-sensitivity testing
ANS: A, B, D
Prenatal testing is conducted before or during the pregnancy but not once labor begins.
Such diagnostic studies include amniocenteses, CVS, and PGD. The correct options are
the only ones that are exclusively used during the prenatal period.
PTS: 1 REF: Page 136 | Box 4-1
Match the genetic terms with the corresponding diseases. Terms may be used more than once. \_\_\_\_\_\_ A. Autosomal dominant \_\_\_\_\_\_ B. Autosomal recessive \_\_\_\_\_\_ C. X-linked dominant \_\_\_\_\_\_ D. X-linked recessive 37. Cystic fibrosis 38. Duchenne muscular dystrophy 39. Sickle cell disease 40. Huntington disease
- ANS: B PTS: 1 REF: Page 154
MSC: Is an important example of an autosomal recessive disease is cystic fibrosis. - ANS: D PTS: 1 REF: Page 158
MSC: Is an important example of an X-linked recessive disease is Duchenne muscular dystrophy. - ANS: B PTS: 1 REF: Page 136 | Box 4-1
MSC: Is an important example of an autosomal recessive disease is sickle cell disease. - ANS: A PTS: 1 REF: Page 154
MSC: Another well-known autosomal dominant disease is Huntington disease.
