Bios 1700 Chapter 14
In what situation can a harmful deletion in a chromosome persist in a population?
if the homologous chromosome lacks the deletion
Which kind of damage to DNA can be caused by X-rays?
breaks in one or both of the sugar-phosphate backbones
If an organism is treated with a chemical agent that doubles the rate of mutation observed in its absence, and a mutation occurs, what is the probability that it was caused by the chemical agent?
1/2
It has been estimated that the average human gamete contains about 30 new nucleotide-substitution mutations and approximately 3 new small insertions or deletions (indels). Assuming a human genome size of 3 x 109 base pairs, what is the estimated rate of nucleotide-substitution mutations and of indel mutations per nucleotide pair per generation?
10-8; 10-9
There is a copy-number variation (CNV) in the human AMY1 gene that encodes a starch-degrading enzyme. If a homozygous genotype with only one copy of AMY1 in each homologous chromosome produces 1 mg/mL of salivary enzyme, what amount of enzyme would be expected in a heterozygous individual with three copies of the AMY1 gene in one chromosome and two copies of AMY1 in the homologous chromosome?
2.5 mg/mL
In the sickle-cell anemia mutation, the 5'-GAG-3' codon for glutamic acid becomes the 5'-GUG-3' codon for valine. Assuming a single nucleotide substitution accounts for this mutation, what is the change in the DNA?
3'-CTC-5'/5'-GAG-3' to 3'-CAC-5'/5'-GTG-3'
When the DNA sequence of the gene that codes for the peptide hormone insulin is compared in two mammals (e.g., humans and rats), most of the sequence differences are synonymous mutations. These far outnumber sequence differences that result in amino acid substitutions. Why might this be?
Amino acid substitutions often result in proteins that have lost or compromised function and, therefore, are selected against.
The enzyme _____ repairs breaks in the DNA sugar-phosphate backbone.
DNA ligase
The enzyme _____ repairs 99% of mismatched bases immediately during DNA replication.
DNA polymerase
Which of the statements most accurately describes the benefits of the proofreading function of DNA polymerase?
DNA polymerase can repair most mutations as they occur during DNA replication.
Which of the statements applies to frameshift mutations?
Frameshift mutations change the amino acid sequence downstream from the site of the mutation.
Which of the statements explains the fact that humans have a relatively large number of mutations per genome per generation when compared to other organisms?
Most of a human's DNA is noncoding, so most of the mutations are neutral.
Imagine that you are a detective who has identified a suspect in a homicide. You acquire a small amount of blood from the crime scene and hand it over to your lab. The lab carries out PCR for one polymorphism, and it returns as a match to your suspect. Is this enough to arrest your suspect?
No, your lab should assess additional polymorphisms; a single polymorphism does not constitute a DNA fingerprint.
Why do data on observable mutant phenotypes underestimate the actual frequency of mutation? Select all that apply.
Some mutations in protein-coding regions of the genome are synonymous mutations. Many mutations are in noncoding regions of the genome.
After using PCR on the same region from two individuals, you notice that each person's DNA yielded pieces of different sizes. Which of the answer choices is the most likely explanation?
The DNA analyzed contains tandem repeats.
The ability to perceive a bitter taste from certain chemicals, including PTC, has been linked to certain alleles. Which of the answer choices would provide an explanation for the fact that almost all nonhuman primates have the "taster" phenotype, whereas the human population has a significant percentage of "nontaster" phenotypes?
The advantage to being able to taste bitter compounds would keep you from eating poisonous compounds, an advantage no longer as strongly selected for in the human population.
Until 20 or 30 years ago, people with cystic fibrosis (CF) would not live long enough to reproduce. CF is a homozygous recessive condition, which led researchers to think that over time the incidence of CF would decrease because the allele would be removed from the gene pool. Statistics on CF actually indicate that the rate of CF is on the rise. Based on what you know about why certain genotypes and phenotypes persist in a population, which of the answer choices could be a likely explanation for why the rate of CF is on the rise?
The heterozygous condition is beneficial, much like what we see with sickle cell trait.
The human genome contains a family of genes that code for different forms of myosin. How could this gene family have arisen?
The original myosin gene was duplicated and the resulting copies have diverged.
Genetic studies have identified an allele (Δ32) that seems to provide protection against HIV. Which of the answer choices would explain the reason why our population has this mutation?
This mutation likely benefited the human population against some other related pathogen.
Genetic studies have identified an allele (Δ32) that seems to provide protection against HIV. This allele is known to exist in the human population before HIV appeared. Which of the answer choices would explain the reason why our population has this mutation?
This mutation likely benefited the human population against some other related pathogen.
Which of the types of mutation is likely to be the most harmful?
deletion of the centromere
Which of the statements concerning cancer and mutations is correct?
Usually multiple mutations are required in different genes to cause cancer.
Why do RNA viruses and retroviruses have such high rates of mutation?
Viral polymerases lack a proofreading mechanism.
A family can share a genetic risk of developing cancer if:
a germ-line mutation in one of the genes implicated in the cancer occurred in an ancestor.
The most frequent kind of mutation, a point mutation, occurs when:
a single base pair is replaced by another.
The nonmutant allele of the BRCA1 gene helps to suppress tumor formation in women who are heterozygous for the mutation. Women heterozygous for BRCA1 nevertheless have a 50% to 70% chance of developing breast cancer before age 70, and the usual reason is that the nonmutant allele is lost or inactivated in a lineage of cells. One possible mechanism for such "loss of heterozygosity" is:
a somatic mutation in a breast cell inactivates the nonmutant BRCA1 allele.
Some people with blue eyes have a small sector of one eye that is brown. What kind of mutation could cause this color difference?
a somatic mutation late in development
Which of the mutations would most likely have the least severe consequences?
addition of three nucleotides
Insertions and deletions of single nucleotides:
cause frameshift mutations.
A nonsense mutation:
changes a codon for an amino acid into a stop codon.
Deletions that eliminate a multiple of three nucleotides can:
delete amino acids in a polypeptide chain.
New genes evolve from:
duplication and divergence.
You are working in a lab studying a gene and notice that there are many other genes in the same organism that code for similar proteins. This is most likely the result of:
duplication and divergence.
A chromosomal mutation where a segment breaks off, flips, and then reattaches itself is called a(n):
inversion.
Chromosomal mutations in which the normal order of a block of genes is reversed is called a(n):
inversion.
Ultraviolet light is a mutagen, but humans need some exposure to it in order to synthesize vitamin D3. The amount of ultraviolet light that penetrates the skin depends on the skin's pigmentation; more melanin (skin pigment) means less penetration. Certain mutations result in decreased melanin production. Such mutations:
may be harmful in one environment and beneficial in another.
Large chromosomal inversions can cause problems in which of these processes?
meiosis
Which type of repair is a backup for the DNA polymerase proofreading function?
mismatch repair
Imagine a gene in which the sequence that is transcribed has a GAG codon, which specifies glutamic acid. If the codon mutated to GUG, which specifies valine, what type of mutation would it be?
missense
A point mutation that creates a premature stop codon is called a _____ mutation.
nonsense
Point mutations can impair a protein if they result in which of the answer choices? Select all that apply.
nonsense codon nonsynonymous codon shift in reading frame
A point mutation that causes an amino acid replacement is called a:
nonsynonymous (missense) mutation.
Which of the point mutations is unlikely to change a protein's ability to function? Select all that apply.
one that occurs in a noncoding region of DNA one that creates a new codon code for the same amino acid as the original codon
"Any genetic difference among individuals that is present in multiple individuals in a population" is the definition of a(n):
polymorphism.
Chronic myelogenous leukemia (CML) is caused when a segment of chromosome 9 and a segment of chromosome 22 both break off and switch places. What type of mutation is this?
reciprocal translocation
When nonhomologous chromosomes exchange parts, a(n) _____ has occurred.
reciprocal translocation
The human genome contains a family of genes that code for different forms of myosin, which are expressed in different cell types and have somewhat different functions. Where in the sequence of each gene would you expect to see differences among them?
regulatory and protein-coding regions
Mutations that affect only the individual in which they occur are called _____ mutations; _____ mutations are passed from parent to offspring.
somatic; germ-line
A point mutation that causes no change in the amino acid sequence of a protein is called a:
synonymous (silent) mutation.
A match between the DNA in a sample and the genomic DNA of a particular individual for a single tandem repeat site is not sufficient to establish identity. However, a mismatch is definitive. The primary reason is that:
the DNA in the sample must match its origin.
The process of gene duplication and divergence refers to which answer choices? Select all that apply.
the creation of gene families, which are similar genes within a species creating new genes by mutation in duplicates of old genes
Normally, in corn, genes for waxy and virescent kernel appearance are located in the same chromosome. In a certain stock, however, it was found that these two genes are in different chromosomes. Which chromosomal aberration would explain this?
translocation
DNA sequences that are capable of moving from place to place in the genome are called:
transposable elements.
A chemical agent that interferes with DNA repair may be considered a mutagen.
true
A chromosomal mutation in which a segment is missing is called a deletion.
true
Cancer is usually due to a series of mutations that occur in a single lineage of somatic cells.
true
Only germ-line mutations are transmitted to progeny.
true