CHAPTER 4
Concept check questions (in figure legends)
FIGURE 4.1
Concept check: What is the difference between the X-Y and X-0 systems of sex
determination?
Answer: In the X-Y system, the presence of the Y chromosome causes maleness,
whereas in the X-0 system, it is the ratio between the number of X chromosomes and
number of sets of autosomes that determines sex. A ratio of 0.5 is male and 1.0 is female.
FIGURE 4.2
Concept check: Is the male bee produced by sexual reproduction? Explain.
Answer: A male bee is not produced by sexual reproduction because it is produced from
an unfertilized egg. Sexual reproduction involves the union of gametes.
FIGURE 4.3
Concept check: How might global warming affect alligator populations?
Answer: A high temperature would favor a high percentage of female alligators. This
might limit population size if there are insufficient numbers of males for reproduction.
On the other, a high number of females might favor a larger population size if males are
not limiting.
FIGURE 4.4
Concept check: Which are the opposite sexes in dioecious plants, the sporophytes or the
gametophytes.
Answer: The sporophytes are the opposite sexes in dioecious plants.
FIGURE 4.5
Concept check: Why is the Barr body more brightly staining in a cell nucleus?
Answer: The Barr body is more brightly staining because it is very compact.
FIGURE 4.6
Concept check: At which stage of development does X inactivation initially occur?
Answer: X inactivation initially occurs during embryonic development.
FIGURE 4.7
Concept check: Which of these phases occurs in an adult female?
Answer: Only the maintenance phase occurs in an adult female.
FIGURE 4.8
Concept check: Why are the homologous regions of the X and Y chromosome important
during meiosis?
Answer: Homologous regions of the X and Y chromosome are important for
chromosome synapsis (pairing) during meiosis.
FIGURE 4.9
Concept check: What is the key result that suggests an X-linked inheritance pattern?
Answer: In the F2 generation, only the males had white eyes.
FIGURE 4.10
Concept check: What features of this pedigree indicate that the allele for Duchenne
muscular dystrophy is X-linked.
Answer: The key pedigree feature that points to X-linked inheritance is that only males
are affected with the disorder. Also, carrier females often have affected brothers.
FIGURE 4.11
Concept check: Explain why the reciprocal cross yields a different result compared to the
first cross.
Answer: The reason why the reciprocal cross yields a different result is because females
carry two copies of an X-linked gene whereas males have only one.