chapter 12 mastering genetics- mutation

Polydactyly is a human autosomal dominant condition that produces extra fingers and toes. Studies of hundreds of families with polydactyly have determined that penetrance for the dominant allele is 70%. Hospital-based surveys of live births find that 1 in 40,000 infants has a new case of polydactyly. Use this information to estimate the mutation rate of the gene.

1 in 56,000 gametes

A wild-type culture of haploid yeast is exposed to ethyl methanesulfonate (EMS). Yeast cells are plated on a complete medium, and 6 colonies (colonies numbered 1 to 6) are transferred to a new complete medium plate for further study. Four replica plates are made from the complete medium plate to plates containing minimal medium or minimal medium plus one amino acid (replica plates numbered 1 to 4) with the following results: Identify the colonies that are prototrophic (wild type). What growth information leads to your answer? Identify the colonies that are auxotrophic (mutant). What growth information leads to your answer? Identify any colonies that are His-, Arg-, Leu- Choose the appropriate genotypes for the following colonies, (choose "+" for the wild-type synthesis and " -" for the mutant synthesis of arginine, histidine, and leucine). Are there any colonies for which genotype information cannot be determined? If so, which colony or colonies?

1,4 The colonies are able to grow on minimal medium containing no additional supplements 2,3,5,6 The colonies are not able to grow on minimal medium containing no additional supplements. His-3 Arg-2 Leu-5 Other colonies-6,1,4 1= + + + 3= - + + 5= + + - 6

Which of the following events could result in a frameshift mutation?

A base deletion would shorten the DNA sequence and change the reading frame of the mRNA.

Which of the following statements regarding Nucleotide Excision Repair (NER) and Base Excision Repair (BER) is true?

Both NER and BER involve the removal of one or more damaged bases by a nuclease.

For 5BU to cause a transition mutation, which of the following must occur?

DNA with incorporated 5BU must replicate. 5BU must undergo a form change, but that is not sufficient to cause transition. The form change must be followed by replication.

What are the examples of chemical mutagens?

EMS hydroxylamine

Which type of mutation results in a string of altered amino acids at the end of the polypeptide product?

Frameshift

If a segment of DNA were replicated without any errors, the replicated strand would have the following sequence of nucleotides: 5' - ACTACGTGA - 3' Sort the following replicated DNA sequences by the type of point mutation each contains (frameshift, base substitution, or neither), as compared to the correct sequence shown above. Sort the items into the appropriate bins.

Frameshift Mutation) 5'-ACTTACGTGA-3' 5'-ACTCGTGA-3" Base substation mutation 5'- ACTAAGTGA-3' 5'-ACTACGTGT-3' neither A base substitution mutation can occur if the DNA polymerase inserts the wrong nucleotide base as it synthesizes a new strand of DNA. A frameshift mutation can occur if the DNA polymerase leaves out a nucleotide or adds an extra nucleotide to the sequence. Certain forms of cancer occur because of mutations in DNA sequences that are located in so-called mutational hotspots. These hotspots are locations in the DNA sequence where mutations occur more often than in other places.

What type of mutation results in a single amino acid substitution?

Missense

Bypass (or translesion) DNA polymerases in E. coli are unique in their ability to do which of the following?

Replicate across DNA damage that stalls DNA pol III.

In a series of 50000 consecutive live births recorded in a large metropolitan area, how many new cases of each disease are expected? Consider using the following equation: (mutation rate × number of births × 2 gametes) / birth

Retinoblastoma, achondroplasia, neurofibromatosis = 2,8,22

The Ames test is used to determine the potential mutagenicity of test compounds by screening for new mutations in which of the following organisms?

Salmonella typhimurium

Which nucleotide will base‑pair with the enol form of 5‑bromouracil?

The enol form of 5‑bromouracil forms a base pair with guanine.

What are the consequences of having pyrimidine dimers in DNA?

These dimers distort the DNA structure and result in errors during DNA replication.

Which type of DNA damage is repaired by the enzyme photolyase?

Thymine dimers.

Thymine dimers are most commonly caused by which of the following?

U.V. irradiation

In terms of its involvement in mutagenesis, 5BU is best described as _______.

a base analog that can cause either A-T > G-C or G-C > A-T transitions In its common form, 5BU can pair with adenine and in its rare form it can pair with guanine.

Generally speaking, which of the following mutations would most severely affect the protein coded for by a gene?

a frameshift deletion at the beginning of the gene A frameshift mutation at the beginning of a gene would affect every codon after the point where the mutation occurred. During protein synthesis, incorrect amino acids would be inserted from the point where the frameshift mutation occurred on; the resulting protein would most probably be nonfunctional. For this reason, a frameshift mutation at the beginning of a gene is generally the most severe type of mutation.

Label the four mutated DNA segments shown below according to the type of point mutation each represents. Use the codon table above to determine how each mutation would affect the amino acid coding for each segment. Drag the labels to their appropriate locations to identify the type of point mutation shown.

a) silent mutation b) nonsense mutation c) missense mutation d) Frameshift mutation Point mutations in DNA sequences can profoundly affect protein synthesis, or they can have no effect at all. Point mutations can be beneficial to an organism but are more commonly neutral or harmful.

What kinds of gene mutations are induced by chemical mutagens?

all of above- transversions frameshifts transitions

What kinds of gene mutations are induced by radiation energy?

all of above- transversions transitions

How is homologous recombination initiated in eukaryotes?

by a double-strand break in one homolog

Which of the following spontaneous changes in DNA structure/sequence generally results from strand slippage?

expansion of trinucleotide repeat sequences

What process gives rise to aberrant 5:3 phenotype ratios in fungal asci?

heteroduplex formation followed by repair

To use RFLP analysis to detect a SNP, the SNP must _______.

occur within a restriction enzyme recognition sequence Addition or removal of a restriction site by a SNP will result in DNA fragments of different lengths (RFLPs) upon restriction enzyme digestion.

In the Ames Test, the appearance of his+ revertants in the presence of a non-mutagenic control compound indicates that _______.

some of the reversion mutations are not caused by the mutagen being tested His+ revertants on the control plate are the result of spontaneous mutation.

The purpose of the Ames Test is to _______.

test the mutagenic effects of chemicals The Ames test detects whether a given chemical can cause a reversion mutation in his- bacteria.

One advantage of allele-specific oligonucleotide (ASO)-based over RFLP-based detection of human genetic disease is that _______.

the mutation need not be located within a restriction enzyme recognition site

Molecular tests for Huntington's disease, cystic fibrosis, and Tay-Sachs disease are possible because _______.

there has been sufficient information gathered on the DNA sequences of both the mutant and normal alleles This information has allowed us to develop tests to detect the DNA changes associated with these diseases.

Many chemicals are more mutagenic after being processed in the liver.

true

Thymine dimers can be repaired by Photoreactivation Repair or Nucleotide Excision Repair

true Both Photoreactivation Repair and Nucleotide Excision Repair will target UV-induced pyrimidine dimers in DNA.

In its rare form, 5BU pairs with guanine.

true In its more common form, 5BU will pair with adenine. In its rare form, it pairs with guanine.

Tautomers of nucleotide bases are isomers that differ from each other in the location of one hydrogen atom in the molecule.

true Nucleotide tautomers differ only in the bonding location of one hydrogen atom.

What are the examples of radiant energy that cause mutations?

γ radiation UVradiation