Ch. 5 Concept Check & Comprehension Questions

Question 1

A female that coils to the left has offspring that coil to the right. What are the genotypes of the mother of these offspring and the maternal grandmother, respectively?

Answer 1

Dd, dd

Question 2

What is the molecular explanation for maternal effect?

Answer 2

• during oogeneis, nurse cells transfer gene products to the oocyte
• the gene products from nurse cells are needed during the very early stages of development

Question 3

In fruit flies, dosage compensation is achieved by..

Answer 3

Turning up the expression of genes on the single X chromosome twofold in the male

Question 4

According to the Lyon hypothesis,

Answer 4

One of the X chromosomes is converted to a Barr body in somatic cells of female mammals

Question 5

Which of the following is not a phase of XCl?
A. Initiation
B. Spreading
C. Maintenance
D. Erasure

Answer 5

D. Erasure

Question 6

In mice, the copy of the Igf2 gene that is inherited from the mother is never expressed in her offspring. That happens because the Igf2 gene from the mother..

Answer 6

Is not transcribed in the somatic cells of the offspring

Question 7

A female mouse, Igf2 lgf2-, is crossed to a male that is also lgf2 lgf2-. The expected outcome of the offspring for this cross is..

Answer 7

1 normal - 1 dwarf

Question 8

The marking process for genomic imprinting initially occurs during..

Answer 8

Gametogenesis

Question 9

A female born with Angelman syndrome carries a deletion in the AS gene. Which parent transmitted the deletion to her?

Answer 9

Her mother

Question 10

Extranuclear inheritance occurs due to..

Answer 10

Genetic material that is found in chloroplasts and mitochondria

Question 11

A cross is made between a green four-o’clock and a variegated four-o’clock. If the variegated plant provides the pollen, the expected outcome of the offspring would be..

Answer 11

All plants with green leaves

Question 12

Some human diseases are caused by mutations in mitochondrial genes. Which of the following statements is false?
A. Human mitochondrial diseases follow a maternal inheritance pattern
B. Mutations associated with mitochondrial diseases often affect cells with a high demand for ATP.
C. The symptoms associated with mitochondrial diseases tend to improve with age.
D. Heteroplasmy plays a key role in the severity of disease symptoms.

Answer 12

C.

Question 13

Chloroplasts and mitochondria evolved from an endosymbiotic relationship involving..

Answer 13

Cyanobacteria and purple bacteria, respectively

Question 14

Experiment showing the inheritance pattern of snail cooking

Explain why all of the offspring in the F2 generation are dextral even though some of them are dd.

Answer 14

Because all of the F1 mothers are Dd, and the genotype of the mother determines the phenotype of the offspring

Question 15

If a mother is heterozygous, Dd, which gene products will the oocyte receive?

Answer 15

The egg cell will receive both D and d gene products.

Question 16

Why is the Barr body more brightly staining in a cell nucleus than the other chromosomes?

Answer 16

Because it is very compact

Question 17

The mechanism of X-chromosome inactivation

At which stage of development does XCl initially occur?

Answer 17

During embryonic development

Question 18

Why do these two forms of G-6-PD migrate differently?

Answer 18

Because their amino acid sequences are slightly different

Question 19

What is the function of the Tsix gene?

Answer 19

It is involved in choosing the X chromosome that is not inactivated

Question 20

Which of these phases occurs in an adult female?
A. Initiation
B. Spreading
C. Maintenance

Answer 20

Only the maintenance phase occurs in an adult female

Question 21

An example of genomic imprinting in the mouse

What would be the outcome of a cross between a heterozygous female and a male that carries two normal copies of the lgf2 gene?

Answer 21

All of the offspring would be normal because they would inherit an active copy from their father.

Question 22

Explain why the erasure phase of imprinting is necessary in eggs.

Answer 22

Erasure allows eggs to transmit unmethylated copies of the gene to the offspring.

Question 23

What is the difference between maintenance methylation and de novo methylation? In what cell types do they occur?

Answer 23

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 germ-line cells.

Question 24

On the left side of this figure, explain why the offspring does not have Prader-Willi syndrome but does have Angelman syndrome.

Answer 24

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.

Question 25

How is a nucleoid different from a cell nucleus?

Answer 25

A nucleoid is not surrounded by a membrane as is the cell nucleus.

Question 26

Why do mitochondria need rRNA and tRNA genes?

Answer 26

To translate proteins within the mitochondrial matrix

Question 27

What is a reciprocal cross?

Answer 27

A cross in which the sexes and phenotypes of the parents are reversed compared to a first cross

Question 28

During growth, can a patch of tissue with a white phenotype give rise to a patch with a green phenotype? Explain.

Answer 28

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.

Question 29

How have chloroplasts and mitochondria changed since the initial endosymbiosis events, which occurred hundreds of millions of years ago?

Answer 29

Chloroplast and mitochondrial genomes have lost most of their genes during evolution. Many of these have been transferred to the cell nucleus.