CHAPTER 5
Concept check questions (in figure legends)
FIGURE 5.1
Concept check: Why are both of these colors considered to be wild type?
Answer: Both of these colors are considered wild type because both of them are prevalent
in natural populations.
FIGURE 5.2
Concept check: Does a PP individual produce more of the protein encoded by the P gene
than is necessary for the purple phenotype?
Answer: Yes. The PP homozygote probably makes twice of the protein that is needed for
purple pigment formation.
FIGURE 5.3
Concept check: Which individual(s) in this pedigree exhibit(s) incomplete penetrance?
Answer: Individual III-2 shows incomplete penetrance.
FIGURE 5.4
Concept check: What are the two main factors that determine an organism’s traits?
Answer: Genes and the environment determine an organism’s traits.
FIGURE 5.5
Concept check: At the molecular level, what is the explanation for why the flowers are
pink instead of red?
Answer: 50% of the functional enzyme is not enough to give a red color.
FIGURE 5.6
Concept check: At which level is incomplete dominance more likely to be observed—at
the molecular/cellular level or at the organism level?
Answer: It is often easier to observe incomplete dominance at the molecular/cellular
level.
FIGURE 5.7
Concept check: Why does the heterozygote have an advantage?
Answer: In this case, the heterozygote is resistant to malaria.
FIGURE 5.8
Concept check: Which of these three scenarios explains overdominance with regard to
the sickle-cell anemia allele?
Answer: The scenario show in part (a) explains the effects of the sickle-cell allele.
FIGURE 5.9
Concept check: Which allele is an example of a loss-of-function allele?
Answer: The i allele is a loss-of-function allele.
FIGURE 5.10
Concept check: Discuss whether these men inherited baldness from their mother or father
or both?
Answer: You can’t really be sure if these men inherited the baldness allele from their
mother or father. If the bald fathers are heterozygotes, they could pass either the bald or
nonbald allele to their sons. The mothers may or may not have passed the bald allele to
their sons.
FIGURE 5.11
Concept check: What is the phenotype of a woman who is heterozygous (one bald allele
and one nonbald allele)?
Answer: A heterozygous woman would not become bald.
FIGURE 5.12
Concept check: What is the molecular explanation for sex-limited inheritance?
Answer: Certain traits are expressed only in males or females, possibly due to differences
in the levels of sex hormones or other factors that differ between the sexes.
FIGURE 5.13
Concept check: Why do you think the heterozygote survives with developmental
abnormalites, whereas the homozygote dies?
Answer: The heterozygote has one normal copy of the gene, which allows for
development to proceed in a way that is not too far from normal. Having two mutant
copies of the gene probably messes up development to a degree that is incompatible with
survival.
FIGURE 5.14
Concept check: What do the terms “epistasis” and “complementation” mean?
Answer: Epistasis means that the alleles of one gene mask the phenotypic effects of the
alleles of a different gene. Complementation occurs when two strains exhibiting the same
recessive trait produce offspring that show the dominant (wild-type) trait. This usually
means the alleles for the recessive trait are in two different genes.
FIGURE 5.15
Concept check: Explain why a single gene knockout does not have an effect on the
phenotype?
Answer: In some cases, a single gene knockout does not have an effect due to gene
redundancy. Other explanations are also possible.
FIGURE 5.16
Concept check: At the molecular level (with regard to loss-of-function alleles), explain
why the ttvv homozygote has an ovate capsule phenotype?
Answer: The two genes are redundant. Having one normal copy of either gene produces a
triangular capsule. If both genes are inactive, an ovate capsule is produced.