Chapter 6: Genetic and Developmental Disorders

Chapter 6: Genetic and Developmental Disorders

Complete Chapter Questions With Answers

Sample Questions Are Posted Below

MULTIPLE CHOICE
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 female’s having a 25% chance of being affected.
d. affected fathers’ transmitting the gene to all their sons.
ANS: A
All daughters of affected fathers are carriers. X-linked (sex-linked) disorders affect primarily males. A carrier female has 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.
b. conception.
c. the first trimester.
d. the last trimester.
ANS: C
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.
ANS: C
PKU is not a chromosome abnormality, but instead a single-gene abnormality often referred to as inborn 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.
ANS: B
As an autosomal recessive disorder, the mating of two carriers (heterozygous) results in a 1 in 4 chance of producing an affected
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 in a 1 in 4
chance of producing an affected offspring and a 2 in 4 chance of producing an offspring who carries the disease. One can predict 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.
ANS: C
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 will 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.