Open Question
The partial amino acid sequence of a wild-type protein is… Arg-Met-Tyr-Thr-Leu-Cys-Ser …The same portion of the protein from a mutant has the sequence… Arg-Met-Leu-Tyr-Ala-Leu-Phe …Identify the type of mutation.
17. Mutation, Repair, and Recombination
Types of Mutations
Back17. Mutation, Repair, and Recombination
Types of Mutations
- Open Question
Speculate on how improved living conditions and medical care in the developed nations might affect human mutation rates, both neutral and deleterious.
- Open QuestionThe two DNA and polypeptide sequences shown are for alleles at a hypothetical locus that produce different polypeptides, both five amino acids long. In each case, the lower DNA strand is the template strand:allele A₁ 5′. . . ATGCATGTAAGTGCATGA. . . 3′3′. . . TACGTACATTCACGTACT. . . 5′A₁ polypeptide N–Met–His–Val–Ser–Ala–Callele A₂ 5′. . . ATGCAAGTAAGTGCATGA . . . 3′3′. . . TACGTTCATTCACGTACT . . . 5′A₂ polypeptide. N–Met–Gln–Val–Ser–Ala–CBased on DNA and polypeptide sequences alone, is there any way to determine which allele is dominant and which is recessive? Why or why not?
- Open QuestionMany human genes are known to have homologs in the mouse genome. One approach to investigating human hereditary disease is to produce mutations of the mouse homologs of human genes by methods that can precisely target specific nucleotides for mutation.Despite the homologies that exist between human and mouse genes, some attempts to study human hereditary disease processes by inducing mutations in mouse genes indicate there is little to be learned about human disease in this way. In general terms, describe how and why the study of mouse gene mutations might fail to produce useful information about human disease processes.
- Open QuestionMany human genes are known to have homologs in the mouse genome. One approach to investigating human hereditary disease is to produce mutations of the mouse homologs of human genes by methods that can precisely target specific nucleotides for mutation.Numerous studies of mutations of the mouse homologs of human genes have yielded valuable information about how gene mutations influence the human disease process. In general terms, describe how and why creating mutations of the mouse homologs can give information about human hereditary disease processes.
- Open Question
The human β-globin wild-type allele and a certain mutant allele are identical in sequence except for a single base-pair substitution that changes one nucleotide at the end of intron 2. The wild-type and mutant sequences of the affected portion of pre-mRNA are
Intron 2 Exon 3 _
wild type 5′-CCUCCCACAG CUCCUG-3′
mutant. 5′-CCUCCCACUG CUCCUG-3′
This is one example of how DNA sequence change occurring somewhere other than in an exon can produce mutation. List other kinds of DNA sequence changes occurring outside exons that can produce mutation. In each case, characterize the kind of change you would expect to see in mutant mRNA or mutant protein. - Open Question
The human β-globin wild-type allele and a certain mutant allele are identical in sequence except for a single base-pair substitution that changes one nucleotide at the end of intron 2. The wild-type and mutant sequences of the affected portion of pre-mRNA are
Intron 2 Exon 3 _
wild type 5′-CCUCCCACAG CUCCUG-3′
mutant. 5′-CCUCCCACUG CUCCUG-3′
Speculate about the way in which this base substitution causes mutation of β-globin protein. - Open QuestionThe fluctuation test performed by Luria and Delbrück is consistent with the random mutation hypothesis. Briefly describe their experiment and identify how the results match the prediction of the random mutation hypothesis. What would have to be different about the experimental results for them to agree with the prediction of the adaptive mutation hypothesis?
- Open Question
Mutations in the CFTR gene result in cystic fibrosis in humans, a condition in which abnormal secretions are present in the lungs, pancreas, and sweat glands. The gene was mapped to a 500-kb region on chromosome 7 containing three candidate genes.
How would you prove that your chosen candidate is the CFTR gene? - Open Question
Mutations in the CFTR gene result in cystic fibrosis in humans, a condition in which abnormal secretions are present in the lungs, pancreas, and sweat glands. The gene was mapped to a 500-kb region on chromosome 7 containing three candidate genes.
Using your knowledge of the disease symptoms, how would you distinguish between the candidate genes to decide which is most likely to encode the CFTR gene? - Open QuestionIn a bacterial culture in which all cells are unable to synthesize leucine (leu⁻), a potent mutagen is added, and the cells are allowed to undergo one round of replication. At that point, samples are taken, a series of dilutions are made, and the cells are plated on either minimal medium or minimal medium containing leucine. The first culture condition (minimal medium) allows the growth of only leu⁺ cells, while the second culture condition (minimal medium with leucine added) allows growth of all cells. The results of the experiment are as follows:Culture Condition Dilution ColoniesMinimal medium 10⁻¹ 18Minimal medium + leucine 10⁻⁷ 9What is the rate of mutation at the locus associated with leucine biosynthesis?
- Open QuestionIn this chapter, three features of genes or of DNA sequence that contribute to the occurrence of mutational hotspots were described. Identify those three features and briefly describe why they are associated with mutational hotspots.
- Open QuestionBriefly compare the production of DNA double-strand breaks in bacteria versus the double-strand breaks that precede homologous recombination.
- Open QuestionImagine yourself as one of the team of geneticists who launches a study of the genetic effects of high-energy radiation on the surviving Japanese population immediately following the atom bomb attacks at Hiroshima and Nagasaki in 1945. Demonstrate your insights into both chromosomal and gene mutation by outlining a short-term and long-term study that addresses these radiation effects. Be sure to include strategies for considering the effects on both somatic and germ-line tissues.
- Open QuestionDuring mismatch repair, why is it necessary to distinguish between the template strand and the newly made daughter strand? Describe how this is accomplished.