Question 1

If a man shows the premutation allele for fragile X syndrome,what is the probability that he will pass it on to his son?

Accepted Answer

Fragile X syndrome is linked to the X chromosome. Since males (XY) pass only their Y chromosome to their sons, a man cannot pass the premutation allele for fragile X syndrome to his son.

Question 2

Assume that a researcher set out to duplicate the Luria-Delbruck fluctuation experiment.This researcher planted twenty small flasks with bacteria from the same colony and let them grow overnight.The next morning the researcher noticed that all but one of the flasks had come open and were ruined.Not wishing to redo the experiment the researcher took bacteria samples from the one remaining intact flask and placed them on twenty phage plates.What results would you expect to see when the twenty phage plates are examined,and how would these results compare with those of the original Luria-Delbruck fluctuation experiment?

Accepted Answer

The researcher's method would not replicate the conditions of the original Luria-Delbruck experiment, which relied on independent bacterial populations to demonstrate mutation rates. By using bacteria from a single flask for all twenty phage plates, any mutations would be shared across all plates, leading to identical numbers of resistant colonies.

Question 3

The term mutation refers to

Accepted Answer

The term mutation refers to a heritable change in the DNA of a cell. While mutations may result in new phenotypes or novel proteins, they can also result in no change or even harmful effects on the cell's survival chances. Therefore, options A, B, and E are not accurate definitions of mutations. Option C is partially accurate, but it does not specify that the change must be heritable.

Question 4

The results of the Luria-Delbruck fluctuation experiment indicated that

Accepted Answer

The Luria-Delbruck fluctuation experiment demonstrated that bacterial resistance to phages arises from random spontaneous mutations, not as a direct response to exposure to phages.

Question 5

The heritable disorder fragile X syndrome,a major cause of mental retardation,is caused by

Accepted Answer

Fragile X syndrome is caused by a mutation in the FMR1 gene, which contains a repeated sequence of three nucleotides (CGG). In individuals with fragile X syndrome, the CGG sequence is repeated many more times than normal, leading to the gene being "turned off" and not producing enough of the FMRP protein. This protein is important for proper brain development and function, and its deficiency leads to the various symptoms of fragile X syndrome, including intellectual disability.

Question 6

A heritable change in DNA base sequence is called a

Accepted Answer

A heritable change in DNA base sequence can be simply defined as a mutation. While a substitution (C) could be considered a type of mutation, it is more specific and only refers to the replacement of one nucleotide with another. A deletion (D) is also a type of mutation but specifically involves the loss of one or more nucleotides in a DNA sequence. A forward mutation (A) refers to a change in the DNA sequence that alters the coding of a gene, while a reversion (B) is a specific type of forward mutation where a mutated gene returns to its original sequence. Therefore, the best answer for a heritable change in DNA base sequence is E, mutation.

Question 7

A mutation in which parts of two nonhomologous chromosomes change places is called a(n)

Accepted Answer

A reciprocal translocation is defined as a chromosomal mutation where parts of two nonhomologous chromosomes exchange places, resulting in the rearrangement of genetic material.

Question 8

UV light is a mutagen that can cause

Accepted Answer

UV light is known to cause thymine dimers, which are covalent bonds between adjacent thymine bases in DNA. Thymine dimers can lead to errors during DNA replication and transcription, potentially causing mutations. Depurination, deamination, alkylation, and oxidation are all DNA damage types caused by different types of mutagens, but they are not typically associated with UV light exposure.

Question 9

Unequal crossing over results in

Accepted Answer

Unequal crossing over can result in a misalignment of homologous chromosomes, leading to a deletion on one chromosome and a duplication on the other. This can result in an unequal distribution of genetic material in the resulting gametes.

Question 10

Consider the following results.When 50 million sperms were examined for a specific mutation,100 mutations were found.Indicate the mutation rate for that gene.

Accepted Answer

The mutation rate is the number of mutations divided by the number of sperm examined. In this case, it would be 100/50,000,000 which simplifies to 2x10^-6, which matches option C.

Question 11

The hydrolysis of a purine base from the deoxyribose-phosphate backbone is called

Accepted Answer

Hydrolysis of a purine base from the deoxyribose-phosphate backbone is called depurination. This leaves an abasic site (AP site) in the DNA molecule.

Question 12

Replacing an adenine nucleotide with a guanine is an example of a

Accepted Answer

Replacing an adenine nucleotide with a guanine is an example of a transition, which involves the substitution of one purine for the other or one pyrimidine for the other. Translocation involves the exchange of genetic material between non-homologous chromosomes, transversion involves the substitution of a purine for a pyrimidine or vice versa, forward mutation results in a change from the wild-type phenotype to a new phenotype, and reversion or reverse mutation involves the restoration of the wild-type phenotype from a mutated phenotype.

Question 13

Thymine dimers are caused by

Accepted Answer

Thymine dimers are formed by the covalent linkage of adjacent thymine bases in DNA when it is exposed to UV radiation, specifically the 254-nm wavelength of UV light. The energy from the UV light causes a rearrangement of the chemical bonds in the thymine bases, creating a covalent bond between the two adjacent thymines, which distorts the DNA structure and impairs DNA replication and transcription. The other options, including X-rays, free radicals, chemicals like EMS or NSG, and depurination, can cause DNA damage, but they do not directly lead to the formation of thymine dimers.

Question 14

The duplication of the triplet sequence CGG resulting in elongation or breakage of the X chromosome is termed

Accepted Answer

The duplication of the triplet sequence CGG is associated with fragile X syndrome, a genetic disorder that can cause intellectual disability and behavioral problems. This duplication can lead to elongation or breakage of the X chromosome. The other answer choices are not associated with this specific genetic phenomenon.

Question 15

Assume that a wild-type sequence is 5'AGCCTAC3'.Indicate the sequence that might be produced by a transversion.

Accepted Answer

A transversion is a type of point mutation where a purine nucleotide is replaced by a pyrimidine nucleotide or vice versa. In this case, the original sequence has a guanine (purine) at the fourth position, and the only answer choice that has a pyrimidine nucleotide (thymine) at this position is D. Therefore, D is the best choice for a sequence produced by a transversion.

Question 16

Which type of mutation is least likely to revert?

Accepted Answer

Deletions are least likely to revert because they involve the removal of nucleotides, making it difficult to restore the original sequence without additional mutations.

Question 17

Assume that the mutation rate for a given gene is 5 × 10^-6 mutations per gene per generation.For that gene how many mutations would be expected if 10 million sperms are examined?

Accepted Answer

The expected number of mutations is calculated by multiplying the mutation rate (5 × 10^-6) by the number of sperms (10 million), resulting in 50 mutations.

Question 18

Genes on the X chromosome of mammals and Drosophila are particularly suitable for genetic study because

Accepted Answer

Males have only one X chromosome and most genes on the X chromosome behave as if they are haploid. Therefore, any mutations or variations on the X chromosome are more easily observed and can have significant effects in males. This makes genes on the X chromosome particularly suitable for genetic study in both mammals and Drosophila.

Question 19

In the Luria-Delbruck fluctuation experiment,the bacteria + phage plates showed

Accepted Answer

The Luria-Delbruck fluctuation experiment demonstrated that mutations occur randomly rather than as a response to environmental stress. In the experiment, some plates had no resistant colonies, indicating that they did not experience any mutations, while a few plates had very many resistant colonies, indicating that they experienced many mutations. This demonstrates that mutations occur randomly and not as a result of the environment. Therefore, option B is the correct answer.

Question 20

Replacing a thymine nucleotide with a guanine is an example of a

Accepted Answer

Replacing a pyrimidine (thymine) with a purine (guanine) is an example of a transversion mutation, which involves a change between bases of different size and chemical properties. Transversions are a type of point mutation and are distinct from transitions, which involve a change between bases of the same size and chemical properties. Translocations involve the movement of large segments of DNA between chromosomes, and forward mutations are those that create a new, altered phenotype. Reversions, or reverse mutations, involve a restoration of the original, wild-type phenotype.

Quiz 7: Gene Expression: the Flow of Information From Dna to Rna to Protein