Question 1

Suppose that for a certain gene, nearly 100 percent of the normal level of expression is required to produce the normal phenotype.Based on this requirement, one could predict that a _______ mutation would be _______.

Accepted Answer

A loss of function mutation would be dominant in this scenario because nearly 100 percent of the normal gene expression is required to produce the normal phenotype. If one allele is mutated and loses function, the remaining normal allele cannot compensate, leading to a dominant phenotype.

Question 2

People are often more concerned about germ line mutations than somatic ones because germ line mutations

Accepted Answer

Germ line mutations are those that occur in the reproductive cells and can be passed on to offspring. Somatic mutations, on the other hand, occur in the body's non-reproductive cells and are not passed on to offspring. Therefore, germ line mutations are more concerning because they can affect future generations, whereas somatic mutations are limited to the individual with the mutation.

Question 3

Gain of function mutations

Accepted Answer

Gain of function mutations are dominant mutations that are expressed in mutant cells, resulting in an enhanced or new function of the gene product. They are not expressed in wild-type cells and therefore not dominant in that context. Gain of function mutations can be analyzed in normal conditions and do not require specific environmental signals. They may contribute to cancer development but are not the sole cause of continuous cell division.

Question 4

Suppose that in one cell in your skin, chromosome 14 and chromosome 18 exchange genetic materials.This change is inherited by subsequent cells.This is an example of a _______ mutation that is also a(n) _______.

Accepted Answer

This is a somatic mutation because it occurs in a body cell, not a germ line cell (sperm or egg). It is also a translocation mutation because it involves the exchange of genetic material between chromosomes.

Question 5

Chronic myelogenous leukemia (CML) is usually caused by the oncogene BCR/ABL.This abnormal gene is the product of the fusion of part of a BCR gene with part of an ABL gene.The resulting protein has unregulated tyrosine kinase activity.The BCR and ABL genes are normally found on two different chromosomes, respectively 22 and 9.What type of mutation is required to generate the BCR/ABL fusion gene?

Accepted Answer

The fusion of BCR gene with ABL gene requires a chromosomal translocation, which is an event during which two chromosomes exchange segments or part of their genetic material. In the case of chronic myelogenous leukemia, this results in the fusion of the two genes on chromosome 9 and 22, respectively, producing the BCR/ABL fusion gene. Chromosomal inversions, deletions, transversions, or transitions do not involve the exchange of segments between chromosomes and would not generate the BCR/ABL fusion gene.

Question 6

If a mutation has a visible effect at 26°C, but no visible effect at 20°C, then 20°C is the _______ temperature and 26°C is the _______ temperature.

Accepted Answer

20°C is the permissive temperature because the organism can live normally despite the mutation. 26°C is the restrictive temperature because the mutation causes a visible effect, indicating the organism is under stress or unable to function normally at this temperature.

Question 7

Sequencing of a child's genomic DNA reveals that the child is a heterozygote for a new mutation.This mutation appears in all of the cells tested from a variety of tissues (including skin, blood, and hair).The mutation is not found in either the mother or the father.Most likely, this is a new _______ mutation that occurred in _______.

Accepted Answer

Since the mutation appears in all of the cells tested from various tissues, it suggests that the mutation is in the germline of the child. As the mutation is not found in either parent, it must have occurred spontaneously during gamete formation in one of the parents. This means that the mutation is a novel germline mutation.

Question 8

Refer to the table.  Alkaptonuria is an inborn error of metabolism, caused by defects in an enzyme in the pathway that breaks down tyrosine (see Section 14.1).Humans who are homozygous for one of these mutations make nonfunctional enzyme and accumulate the enzyme's substrate, homogentisic acid, which causes their disease symptoms.In 1996, researchers in Spain cloned and sequenced the gene for the enzyme and characterized several mutant alleles.The table shows the wild-type coding strand sequence for part of the gene and the corresponding region from one of the mutant alleles.What type of mutation is this?

Accepted Answer

The mutation shown in the table is a missense mutation, which results in a change in a single nucleotide that leads to a change in the corresponding amino acid in the protein sequence. Specifically, the third codon in the wild-type sequence (GCT) is changed to a different codon (ACT) in the mutant sequence, resulting in a different amino acid (threonine instead of alanine) at that position in the protein.

Question 9

Because of the redundancy in the genetic code, many mutations in the coding regions of genes are

Accepted Answer

Due to the redundancy of the genetic code, many mutations may not result in a change to the resulting amino acid sequence. These are known as silent mutations. transitions and transversions are types of substitution mutations that can be either silent or result in a change to the amino acid sequence, and inversions are a type of chromosomal mutation. Somatic mutations occur in non-reproductive cells and are not relevant to the genetic code redundancy. Therefore, the most appropriate answer is E) silent mutations.

Question 10

Refer to the following image.  Given the codon UCA in the first exon of a gene, which change is most likely to result in a nonsense mutation?

Accepted Answer

The answer of Refer to the following image.  Given...

Question 11

In wild type Drosophila melanogaster, the order of genes on a chromosome is yellow, vermillion, forked, and Bobbed.Some of the flies have a different gene order: yellow, Bobbed, forked, and vermillion.The flies with the altered gene order most likely have a

Accepted Answer

The altered gene order in the flies is due to a chromosomal inversion, which means a portion of the chromosome has been reversed. This is the most likely explanation as it would preserve the order of the genes and can occur naturally in Drosophila. None of the other choices would account for the change in gene order.

Question 12

Analysis of the abnormal white blood cells of a patient with leukemia, a type of cancer, reveals that a protein, termed LP, is always functionally active.In normal white blood cells this protein is found to be only functionally active in response to growth stimuli that induce cell division.Surprisingly, sequencing of leukemic cell DNA shows that both LP alleles in the patient's leukemic cells are normal.However, the DNA sequencing also reveals that both alleles of protein ILP, which normally inhibits LP activity in the absence of growth stimuli, have each acquired a mutation.Further research proves that these _______ mutations in both ILP alleles are the reason why LP is always active and, consequently, induces the leukemic cells to constantly undergo cell division.

Accepted Answer

The mutations in both ILP alleles are described as causing the ILP protein to lose its normal function of inhibiting LP activity. This loss of inhibitory function allows LP to remain always active, leading to constant cell division in the leukemic cells. Therefore, these mutations are characterized as loss-of-function mutations.

Question 13

A bacterial cell has been exposed to a powerful mutagen.The chromosomal sequences of the ancestral cell and the descendant cell are shown.(The ellipses represent intervening sequences that are identical.)  Based on this information, there have been _______ transitions and _______ transversions.

Accepted Answer

The answer of A bacterial cell has been exposed to...

Question 14

One son of Great Britain's Queen Victoria was born with the X-linked disease hemophilia, and two of her daughters were carriers, as some of their male children were born with hemophilia.King Albert did not have hemophilia, nor did any of Queen Victoria's relatives on her mother's side.Based on this information, the hemophilia mutation most likely originated

Accepted Answer

Since none of Queen Victoria's relatives on her mother's side had hemophilia, the mutation most likely occurred in a spontaneous mutation (or somatic mutation) in the egg cell from Queen Victoria's mother. King Albert did not have hemophilia and none of Queen Victoria's relatives on her father’s side had hemophilia, eliminating options A, B, C, and E. Therefore, option D is the most likely explanation for the origin of the hemophilia mutation.

Question 15

The isoenzyme hexosaminidase A (HEXA), composed of subunits α and β, breaks down molecules containing terminal N-acetyl hexosamines.Tay-Sachs disease is caused by a recessively inherited mutation in the gene coding for the α subunit, which is the subunit that hydrolyzes the lipid GM2 ganglioside.Accumulation of this lipid in the brain leads to progressive deterioration of the nervous system and death, usually by age 4.A child born homozygous for the loss-of-function α subunit allele nevertheless does not develop Tay-Sachs disease.Sequence analysis of the β subunit alleles reveals that one allele has a mutation that makes it able to hydrolyze GM2 ganglioside.This is a _______-of-function mutation, which is most likely _______.

Accepted Answer

The mutation in the β subunit that allows it to hydrolyze GM2 ganglioside compensates for the loss of function in the α subunit, indicating a gain of a new or enhanced function. This mutation would most likely exhibit a dominant pattern of inheritance because only one copy of the mutated β subunit gene is needed to provide the beneficial function of breaking down GM2 ganglioside, preventing Tay-Sachs disease.

Question 16

Suppose that a mutation appears in a small population of plants that changes the color of their seeds from yellow to green.This mutation reaches 100 percent frequency in the population.Many generations later, some individuals with yellow seeds are found.We can definitely say that these individuals have acquired a(n)

Accepted Answer

The appearance of individuals with yellow seeds after the mutation had reached 100% frequency suggests that a reversion mutation occurred, where the mutation that caused the color change has been reverted back to the original yellow seed color.

Question 17

Which statement about mutations is true?

Accepted Answer

All transitions are a type of point mutation, as they involve a change of a single nucleotide base to another base of the same type (purine to purine or pyrimidine to pyrimidine).

Question 18

Which mutation is least likely to be a frame-shift mutation?

Accepted Answer

An insertion of six nucleotides is least likely to be a frame-shift mutation because it adds a number of nucleotides that is a multiple of three, preserving the reading frame.

Question 19

The functional activity of the KRAS protein promotes cell proliferation and is often mutated in leukemia (cancer of a type of blood cell).In a B cell leukemia, a clinical researcher identifies a G → A transition at the second base of codon 12, resulting in a glycine → aspartic acid substitution in the protein.In normal cells, KRAS protein function can be activated and suppressed by the activity of other proteins.In contrast, in the leukemic cells, KRAS protein function is resistant to suppression.This is an example of a _______ mutation generating a_______-of-function mutation.

Accepted Answer

The mutation described in this scenario is a missense mutation, as it results in a substitution of one amino acid for another. Specifically, the substitution of glycine to aspartic acid at position 12 of the KRAS protein. This mutation results in a gain-of-function mutation, as the KRAS protein function promotes cell proliferation, and the mutation makes it resistant to suppression. Therefore, the best choice is C: missense; gain.

Question 20

Drosophila melanogaster flies that have the Shaker mutation appear normal at room temperature.If you hold a vial of flies with this mutation for a few minutes (i.e., warm the vial to body temperature, or 37^oC), the flies become uncoordinated because of the warmth of your hand.If you remove your hand, the flies soon recover.Based on this information, which statement about the Shaker mutation must be true?

Accepted Answer

The fact that the Shaker mutation causes uncoordination when the flies are warmed to 37°C suggests that the mutation is restrictive at this temperature. This means that the mutation impairs normal function of the potassium channels in the fly's nerve cells, which are responsible for controlling muscle movement. The fact that the flies recover when the temperature returns to room temperature suggests that the mutation is permissive at lower temperatures. This means that the mutation does not impair channel function when the temperature is cooler, allowing the flies to move normally. The other answer choices are incorrect based on the information given.

Quiz 15: Gene Mutation and Molecular Medicine

Suppose that for a certain gene, nearly 100 percent of the normal level of expression is required to produce the normal phenotype.Based on this requirement, one could predict that a _ mutation would be _.

People are often more concerned about germ line mutations than somatic ones because germ line mutations

Gain of function mutations

Suppose that in one cell in your skin, chromosome 14 and chromosome 18 exchange genetic materials.This change is inherited by subsequent cells.This is an example of a _ mutation that is also a(n) _.

If a mutation has a visible effect at 26°C, but no visible effect at 20°C, then 20°C is the _ temperature and 26°C is the _ temperature.

Because of the redundancy in the genetic code, many mutations in the coding regions of genes are

Refer to the following image. Given the codon UCA in the first exon of a gene, which change is most likely to result in a nonsense mutation?

In wild type Drosophila melanogaster, the order of genes on a chromosome is yellow, vermillion, forked, and Bobbed.Some of the flies have a different gene order: yellow, Bobbed, forked, and vermillion.The flies with the altered gene order most likely have a

A bacterial cell has been exposed to a powerful mutagen.The chromosomal sequences of the ancestral cell and the descendant cell are shown.(The ellipses represent intervening sequences that are identical.) Based on this information, there have been _ transitions and _ transversions.

Which statement about mutations is true?

Which mutation is least likely to be a frame-shift mutation?