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Concept explainers
Neurofibromas are tumors of the skin that can arise when a skin cell that is originally NF1+/NF1- loses the NF1+ allele. This wild-type allele encodes a functional protein (called a “tumor suppressor”), while the NF1- allele encodes a nonfunctional protein.
A patient of genotype NF1+</i>/NF1- has 20 independent tumors in different areas of the skin. Samples are taken ofnormal, noncancerous cells from this patient, as well as of cells from each of the 20 tumors. Extracts of these samples are analyzed by a technique called gel electrophoresis that can detect variant forms of four different proteins (A, B, C, and D) all encoded by genes that lie on the same autosome as NF1. Each protein has a slow (S) and a fast (F) form that are encoded by different alleles (for example, AS and AF ). In the extract of normal tissue, slow and fast variants of all four proteins are found. In the extracts of the tumors, 12 had only the fast variants of proteins A and D but both the fast and slow variants of proteins B and C; 6 had only the fast variant of protein A but both the fast and slow variants of proteins B, C, and D; and the remaining 2 tumor extracts had only the fast variant of protein A, only the slow variant of protein B, the fast and slow variants of protein C, and only the fast variant of protein D.
a. | What kind of genetic event described in this chapter could cause all 20 tumors, assuming that all the tumors are produced by the same mechanism? |
b. | Draw a genetic map describing these data, assuming that this small sample represents all the types of tumors that could be formed by the same mechanism in this patient. Show which alleles of which genes lie on the two homologous chromosomes. Indicate all relative distances that can be estimated. |
c. | Another mechanism that can lead to neurofibromas in this patient is a mitotic error producing cells with 45 rather than the normal 46 chromosomes. How can this mechanism cause tumors? How do you know, just from the results described, that none of these 20 tumors is formed by such mitotic errors? |
d. | Can you think of any other type of error that could produce the results described? |
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Chapter 5 Solutions
Genetics: From Genes to Genomes, 5th edition
- The propensity to develop retinal cancer can run in pedigrees of certain families. You have learned about the role of the retinoblastoma (Rb) protein in the cell cycle. A heterozygous individual (genotype = Rbm / Rb+) that inherits a mutant allele of the Rb gene (Rbm) as well as a normal allele of the Rb gene (Rb+) is at significant risk for developing cancer of the retina. The best explanation for this is that… A. the Rb(m) allele is dominant to the Rb(+) allele. B. a mutation in the Rb(+) allele can result in a Rb(m) / Rb(m) genotype in certain cells. C. the retina is frequently exposed to UV rays D. the Rb(m) allele directly converts the Rb(+) allele to another Rb(m) allele. E. the cells of the retina carry more than two copies of the Rb genearrow_forwardThe Xg cell-surface antigen is coded for by a gene located on the X chromosome. No equivalent gene exists on the Y chromosome. Two codominant alleles of this gene have been identified: Xg1 and Xg2. A woman of genotype Xg2/Xg2 bears children with a man of genotype Xg1/Y, and they produce a son with Klinefelter syndrome of genotype Xg1/Xg2Y. Using proper genetic terminology, briefly explain how this individual was generated. In which parent and in which meiotic division did the mistake occur?arrow_forwardMSH2 is a gene commonly associated with HNPCC (Hereditary nonpolyposis colorectal cancer). This gene encodes a protein that is involved in mismatch repair. Why are individuals who are heterozygous for the deletion mutation of MSH2 gene (MSH2+/MSH2-) from birth are very likely to develop colon cancer very early in their lives?arrow_forward
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- "In most differentiated tissues, daughter cells retain a memory of gene expression patterns that were present in the parent cell through mechanisms that do not involve changes in the sequence of their genomic DNA" is true or false.arrow_forwardDuchenne Muscular Dystrophy (DMD) is a disorder that primarily affects the function of skeletal muscles used for movement and cardiac muscles used for heart beating. Dystrophin is a protein encoded by a single gene, DMD, that is expressed in skeletal and cardiac muscle. Some forms of muscular dystrophy may be caused by different mutations in the DNA sequence of the DMD gene. Because the DMD locus is on the X chromosome, males are affected at higher rates. Two brothers, one of whom has DMD and one of whom does not, worked with their genetic counselor (Links to an external site.) to have their DMD gene sequenced to identify genetic variation that may explain why one brother was affected and the other not. Because DMD is a very long gene, a fictionalized, simplified model of the results is presented here (Figure 1). The actual DMD mRNA is about 16,000 base-pairs!------Consider single nucleotide polymorphism (SNP) #1 (Figure 1). Is this mutation likely to cause Duchenne muscular…arrow_forwardIn tumor cells obtained from patients with Burkittlymphoma, a cancer of the immune system’s B cells,the myc gene often appears close to one of the breakpoints of a reciprocal translocation between chromosomes 8 and 14. In this translocated position, myc is expressed at a higher-than-normal level. Scientists hypothesize that Myc protein overexpression in B cellscontributes to lymphoma formation.a. Explain how transgenic mice produced using pronuclear injection could be used to test this hypothesis. (Assume that you previously cloned a generegulatory region that is active specifically in Bcells throughout the life of the mouse.)b. Suppose you wanted to overexpress Myc only inthe immune cells of mice, starting at one week ofage. To restrict Myc transcription spatially, youwill use same promoter described in part (a). Torestrict Myc transcription temporally, you will usea cre transgene whose expression is controlled byheat shock (hs-cre). Describe the mouse you wouldcreate to accomplish…arrow_forward
- The Human papillomavirus (HPV) has been linked to an increased risk of cervical cancer. The HPV E6 and E7 proteins govern the cell via altering cellular proteins. The E6 protein interacts with the tumor suppressor protein p53 and directs its ubiquitin-mediated destruction. Can you elaborate about the P63 gene: its function and if it can be altered/mutated by HPV? If it does, what is the relationship between P53 and P63? Thank you!arrow_forwardThe genotype of a dwarf mouse is Igf2 Igf2–. What is the genotype of its father who has normal body size? Indicate which allele is on the maternal chromosome and which allele is on the paternal chromosome for both dwarf mouse and its father.arrow_forwardSeveral genes in humans in addition to the ABO gene () give rise to recognizable antigens on the surface of the red blood cells. The Rh marker is determined by positive (R) and negative alleles () of gene R, where R is completely dominant to r. The presence of M and N surface proteins are controlled by two codominant alleles of gene L (LM and LM. For each mother-child pair, choose the father of the child from among the males in the right column. (Assume that all mothers and fathers are HH; there is no involvement of the Bombay phenotype.) Paternal genotypes maybe used once, more than once, or not at all. Each mother-child pair matches with one or more than one paternal genotype. Maternal phenotype: Child phenotype: Paternal genotype: Reset A, M, Rh(neg) O, M, Rh(pos) B, N, Rh(neg) O, N, Rh(pos) O, M, Rh(neg) A, MN, Rh(pos) A, N, Rh(pos) AB, MN, Rh(pos) B, N, Rh(pos) A, MN, Rh(neg) Genotypes of possible fathers AiLMLN rr BiLMLN RR ii LNLN rr ii LMLM rr AALMLN RRarrow_forward
- Human Heredity: Principles and Issues (MindTap Co...BiologyISBN:9781305251052Author:Michael CummingsPublisher:Cengage Learning
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