CHAPTER 8
Concept check questions (in figure legends)
FIGURE 8.1
Concept check: Why is it useful to stain chromosomes?
Answer: The staining of chromosomes results in banding patterns that make it easier to
distinguish chromosomes that are similar in size and have similar centromere locations.
FIGURE 8.2
Concept check: Which of these changes alter the total amount of genetic material?
Answer: Deletions and duplications alter the total amount of genetic material.
FIGURE 8.3
Concept check: What is the reason why a chromosomal fragment is lost and then
subsequently degraded?
Answer: If a chromosomal fragment does not contain a centromere, it will not segregate
properly. If it remains outside the nucleus, it will be degraded.
FIGURE 8.5
Concept check: What is the underlying cause of nonallelic homologous recombination?
Answer: Nonallelic homologous recombination occurs because of the pairing of
homologous sites that duplicated within the chromosomes. This pairing causes the
chromosomes to be misaligned.
FIGURE 8.10
Concept check: Explain why these chromosomes form an inversion loop.
Answer: These chromosomes form an inversion loop because the homologous regions
are pairing with each other. For the inverted and noninverted regions to pair, a loop must
form.
FIGURE 8.11
Concept check: Which of these two mechanisms might be promoted by the presence of
the same transposable element in many places in a species genome?
Answer: The mechanism shown in part (b) may occur if transposable elements are found
in different chromosomes. These elements may promote the pairing between
nonhomologous chromosomes and a subsequent crossover could occur.
FIGURE 8.12
Concept check: If these segregation patterns are equally likely, what is the probability
that a gamete made from this individual will result in a viable offspring with a normal
phenotype?
Answer: Two out of six gametes (the two on the left) will produce a viable offspring with
a normal phenotype. Therefore, the probability is 2/6 or 1/3.
FIGURE 8.13
Concept check: Explain why these chromosomes form a translocation cross during
prophase of meiosis I.
Answer: These chromosomes form a translocation cross because homologous regions are
pairing with each other.
FIGURE 8.14
Concept check: What adjectives could be used to describe a fruit fly that has a total of
seven chromosomes because it is missing one copy of chromosome 3.
Answer: aneuploid, monosomic, monosomy 3.
FIGURE 8.15
Concept check: Describe the imbalance that would occur in monosomy 2.
Answer: The genes on chromosome 2 would be found in single copies whereas the genes
on the other chromosomes would be found in two copies. The expression of genes on
chromosome 2 would be less (perhaps 50%) relative to a normal individual. This creates
an imbalance between genes on chromosome 2 and those on the other chromosomes.
FIGURE 8.18
Concept check: Approximately how many copies of chromosome 2 are found in a
polytene chromosome?
Answer: About 512.
FIGURE 8.19
Concept check: What are some common advantages of polyploidy in plants?
Answer: Polyploid plants are often more vigorous and disease resistant. They may have
larger flowers and produce more fruit.
FIGURE 8.20
Concept check: Explain why a triploid individual is usually infertile.
Answer: During meiosis in a triploid individual, the homologs cannot pair properly. This
results in highly aneuploid gametes, which are usually nonviable. Also, if aneuploid
gametes participate in fertilization, the offspring are usually nonviable.
FIGURE 8.21
Concept check: Explain what the word nondisjunction means.
Answer: In this case, nondisjunction means that pairs of chromosomes are not separating
from each other properly.
FIGURE 8.24
Concept check: What is the key difference between autopolyploidy and allopolyploidy?
Answer: In autopolyploidy, multiple sets of chromosomes come from the same species.
In allopolyploidy, multiple sets of chromosomes come from at least two different species.
FIGURE 8.26
Concept check: Which of these two cells, an allodiploid and/or an allotetraploid, is/are
likely to produce viable gametes? Explain why.
Answer: The allotetraploid is more likely to produce viable gametes because the
chromosomes can pair up and produce euploid gametes. By comparison, the allodiploid
will produce aneuploid gametes that are likely to be nonviable.