Download Ch06 Answers to Concept Check Questions

CHAPTER 6
Concept check questions (in figure legends)
FIGURE 6.1
Concept check: How is a nucleoid different from a cell nucleus?
Answer: A nucleoid is not surrounded by a membrane as is the cell nucleus.
FIGURE 6.2
Concept check: With regard to the total number of genes, how does the chloroplast
genome compare to the nuclear genome?
Answer: The chloroplast genome contains about 100 genes whereas nuclear genomes in
plants have several thousand or tens of thousands of genes.
FIGURE 6.3
Concept check: What is a reciprocal cross?
Answer: A reciprocal cross is a cross in which the sexes and phenotypes of the parents
are reversed compared to a first cross.
FIGURE 6.4
Concept check: During growth, can a patch of tissue with a white phenotype give rise to a
patch with a green phenotype? Explain.
Answer: No. Once a patch of tissue is white, it has lost all of the normal chloroplasts, so
it could not produce a patch of green tissue.
FIGURE 6.5
Concept check: In this species, which mating type transmits chloroplasts to offspring?
Answer: The mt+ mating type transmits chloroplasts to the offspring.
FIGURE 6.6
Concept check: Within one nucleoid, is the mitochondrial chromosome found in a single
copy or multiple copies?
Answer: One mitochondrial nucleoid usually contains multiple copies of the chloroplast
genome.
FIGURE 6.7
Concept check: Why do mitochondria need rRNA and tRNA genes?
Answer: Mitochondria need rRNA and tRNA genes to translate proteins within the
mitochondrial matrix.
FIGURE 6.8
Concept check: How have chloroplasts and mitochondria changed since the initial
endosymbiosis events, which occurred hundreds of millions of years ago?
Answer: Chloroplast and mitochondrial genomes have lost most of their genes during
evolution. Many of these have been transferred to the cell nucleus.
FIGURE 6.9
Concept check: What would be the outcome of a cross between a heterozygous female
and a male that carried two normal copies of the Igf2 gene?
Answer: All of the offspring would be normal because they would inherit an active copy
from their father.
FIGURE 6.10
Concept check: With regard to eggs, explain why the erasure phase of imprinting is
necessary.
Answer: Erasure allows eggs to transmit unmethylated copies of the gene to the
offspring.
FIGURE 6.11.
Concept check: What process prevents the binding of CTC-binding factor to the ICR?
Answer: Methylation prevents CTC-binding factor from binding to the ICR.
FIGURE 6.12.
Concept check: What is the difference between maintenance methylation and de novo
methylation? In what cell types (somatic cells or germline cells), do they occur?
Answer: Maintenance methylation is automatic methylation that occurs when a
methylated gene replicates and is transferred to daughter cells. It occurs in somatic cells.
De novo methylation is the methylation of a gene that is not already methylated. It occurs
in germline cells.
FIGURE 6.13
Concept check: On the left side of this figure, explain why the offspring does not have
Prader-Willi syndrome but does have Angelman syndrome.
Answer: The offspring on the left did not receive a copy of either gene from their mother.
Their father silences the AS gene, so they have AS because they do not have an active
copy of the AS gene. By comparison, they receive an active PWS gene from their father,
which prevents them from having PWS.
FIGURE 6.14
Concept check: Explain why all of the offspring in the F2 generation are dextral even
though some of them are dd.
Answer: The offspring are all dextral because all of the F1 mothers are Dd, and the
genotype of the mother determines the phenotype of the offspring.
FIGURE 6.15
Concept check: If a mother is heterozygous, Dd, which gene products will the egg cell
receive?
Answer: The egg cell will receive both D and d gene products.