Chapter 7, Problem 1P

The following is a list of mutational changes. For each of the specific mutations described, indicate which of the terms in the right-hand column applies, either as a description of the mutation or as a possible cause. More than one term from the right column can apply to each statement in the left column.

1. an A-T base pair in the wild-type gene is changed to a G-C pair	a. transition
2. an A-T base pair is changed to a T-A pair	b. base substitution
3. the sequence AAGCTTATCG is changed to AAGCTATCG	c. transversion
4. the sequence AAGCTTATCG is changed to AAGCTTTATCG	d. deletion
5. the sequence AACGTTATCG is changed to AATGTTATCG	e. insertion
6. the sequence AACGTCACACACATCG is changed to AACGTCACATCG	f. deamination
	g. X-ray irradiation
	h. intercalator

Summary Introduction

1.

To determine:

The term that describes “an A-T base pair in the wild-type gene is changed to a G-C pair” among the options given below,

a. transition

b. base substitution

c. transversion

d. deletion

e. insertion

f. deamination

g. X-ray irradiation

h. intercalator

Introduction:

When purines and pyrimidines are exchanged with each other, the process is called transition.

Answer to Problem 1P

Correct answer:

An A-T base pair in the wild-type gene is changed to a G-C pair: transition and base substitution.

Explanation of Solution

In the given mutation, A-T base pair is exchanged with a G-C base pair so it can be a base substitution. This can also be a transition mutation because adenine is a purine which is interchanged with another purine that is guanine. Thymine replaced the cytosine, and both are also pyrimidines. Thus, this condition can be a base substitution mutation or a transition mutation.

Summary Introduction

2.

To determine:

The term that describes “an A-T base pair is changed to a T-A pair” among the options given below,

a. transition

b. base substitution

c. transversion

d. deletion

e. insertion

f. deamination

g. X-ray irradiation

h. intercalator

Introduction:

When one purine is replaced by pyrimidine in a pair of two bases, the resulting process is called transversion.

Answer to Problem 1P

Correct answer:

an A-T base pair is changed to a T-A pair: base substitution and transversion.

Explanation of Solution

In the given mutation, a base pair ‘A-T’ can be changed to a ‘T-A’ base-pair so the replacement of one purine with pyrimidine can be observed. Thus, the mutation for concerting A-T into T-A can be a transversion. The substitution of A by T is taking place so, it can also be a base substitution mutation.

Summary Introduction

3.

To determine:

The term that describes “the sequence AAGCTTATCG is changed to AAGCTATCG” among the options given below,

a. transition

b. base substitution

c. transversion

d. deletion

e. insertion

f. deamination

g. X-ray irradiation

h. intercalator

Introduction:

In this particular case, the exposure of X-rays is responsible for deletion mutation from the wild type sequence.

Answer to Problem 1P

Correct answer:

the sequence AAGCTTATCG is changed to AAGCTATCG: deletion and X-ray irradiation.

Explanation of Solution

If both, wild type and mutated sequence are observed that it can be seen that there is a deletion of nitrogenous base T from wild type sequence. The exposure to X-ray irradiation may be responsible for deletion mutation. Thus, the correct match for the given mutation is deletion and X-ray irradiation.

Summary Introduction

4.

To determine:

The term that describes “the sequence AAGCTTATCG is changed to AAGCTTTATCG” among the options given below,

a. transition

b. base substitution

c. transversion

d. deletion

e. insertion

f. deamination

g. X-ray irradiation

h. intercalator

Introduction:

When one or more nitrogenous bases are removed from the nucleotide sequence, then the process is called deletion.

Answer to Problem 1P

Correct answer:

the sequence AAGCTTATCG is changed to AAGCTTTATCG: deletion and X-ray irradiation.

Explanation of Solution

Observation of wild type and mutated sequence can lead to a conclusion that there is a deletion of nitrogenous base T from wild type sequence. Deletion mutation may happen to because of exposure to X-ray irradiation. Thus, the correct match for the given mutation is deletion and X-ray irradiation.

Summary Introduction

5.

To determine:

The term that describes “the sequence AACGTTATCG is changed to AATGTTATCG” among the options given below,

a. transition

b. base substitution

c. transversion

d. deletion

e. insertion

f. deamination

g. X-ray irradiation

h. intercalator

Introduction:

Transition is the change of one purine to another purine or one pyrimidine to another pyrimidine.

Answer to Problem 1P

Correct answer:

the sequence AACGTTATCG is changed to AATGTTATCG: base substitution, transition, and deamination.

Explanation of Solution

In the given mutation, base T is exchanged with base C so it can be a base substitution. This can also be a transition mutation because cytosine is a pyrimidine which is interchanged with another pyrimidine that is thymine. Deamination can also be noticed in the given mutation because the conversion of a methylated C to T is taking place. Thus, the correct match for the given mutation is a substitution, transition, and deamination.

Summary Introduction

6.

To determine:

The term that describes “the sequence AACGTCACACACATCG is changed to AACGTCACATCG” among the options given below,

a. transition

b. base substitution

c. transversion

d. deletion

e. insertion

f. deamination

g. X-ray irradiation

h. intercalator

Introduction:

Crossing over is the process of exchange of genetic material between the sister chromatids at chiasmata.

Answer to Problem 1P

Correct answer:

The sequence AACGTCACACACATCG is changed to AACGTCACATCG: deletion and crossing over.

Explanation of Solution

In the given mutation, it can be noticed that a segment CACACACA has been lost from wild type sequence, so it is representing deletion. A segment can be removed from the wild type gene during the process of crossing over. Thus, the correct match for the given mutation is deletion and crossing over.