Hartl, Jones - Genetics. Principlers and analysis - 1998 (522927), страница 92
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If assigned to do so, write a one-paragraph description of how this instrument works, and discuss some of itlimitations.3. There are many myths about Down syndrome. One is that people with Down syndrome are severely retarded. Yocan find more myths, and the truth about them, at the keyword site. If assigned to do so, prepare a double-column lisgiving a brief description of each myth and the correct story.MUTABLE SITE EXERCISESThe Mutable Site Exercise changes frequently.
Each new update includes a different exercise that makes use of generesources available on the World Wide Web. Select the Mutable Site for Chapter 7, and you will be linked to thecurrent exercise that relates to the material presented in this chapter.PIC SITEThe Pic Site showcases some of the most visually appealing genetics sites on the World Wide Web. To visit theshowcase genetics site, select the Pic Site for Chapter 7.7.2 An autopolyploid series similar to Chrysanthemum consists of five species. The basic monoploid chromosomenumber in the group is 5. What chromosome numbers would be expected among the species?7.3 A plant species S coexists with two related species A and B. All species are interfertile. In meiosis, S forms 26bivalents, and A and B form 14 and 12 bivalents, respectively.
Hybrids between S and A form 14 bivalents and 12univalents, and hybrids between S and B form 12 bivalents and 14 univalents. Suggest a probable evolutionary origispecies S.7.4 A spontaneously aborted human fetus was found to have the karyotype 92,XXYY. What might have happened to thchromosomes in the zygote to result in this karyotype?7.5 A spontaneously aborted human fetus is found to have 45 chromosomes. What is the most probable karyotype? Hathe fetus survived, what genetic disorder would it have had?7.6 Color blindness in human beings is an X-linked trait. A man who is color-blind has a 45,X (Turner syndrome)daughter who is also color-blind.
Did the nondisjunction that led to the 45,X child occur in the mother or the father? Hocan you tell?7.7 A phenotypically normal woman has a child with Down syndrome. The woman is found to have 45 chromosomesWhat kind of chromosome abnormality can account for these observations? How many chromosomes does the affectechild have? How does this differ from the usual chromosome number and karyotype of a child with Down syndrome?Page 3047.8 A chromosome has the gene sequence A B C D E F G.
What is the sequence following a C-through-Einversion? Following a C-through-E deletion? Two chromosomes with the sequences A B C D E F G and M N O PQ R S T U V undergo a reciprocal translocation after breaks in E–F and S–T. What are the possible products?Which products are genetically stable?7.9 Recessive genes a, b, c, d, e, and f are closely linked in a chromosome, but their order is unknown.
Threedeletions in the region are examined. One deletion uncovers a, d, and e; another uncovers c, d, and f; and the thirduncovers b and c. What is the order of the genes?7.10 Six bands in a salivary gland chromosome of Drosophila are shown in the accompanying figure, along withthe extent of five deletions (Del1–Del5).Recessive alleles a, b, c, d, e, and f are known to be in the region, but their order is unknown. When the deletionsare heterozygous with each allele, the following results are obtained:abcdefDel 1---+++Del 2-+-+++De1 3-+-+-+Del 4++---+Del 5+++---In this table, the - means that the deletion is missing the corresponding wildtype allele (the deletion uncovers therecessive allele) and + means that the corresponding wildtype allele is still present. Use these data to infer theposition of each gene relative to the salivary gland chromosome bands.7.11 A strain of corn that has been maintained by self-fertilization for many generations, when crossed with anormal strain, produces an F1 in which many meiotic cells have dicentric chromatids and acentries, and the amountof recombination in chromosome 6 is greatly reduced.
However, in the original strain, no dicentrics or acentrics arefound. What kind of abnormality in chromosome structure can explain these results?7.12 Four strains of Drosophila melanogaster are isolated from different localities. The banding patterns of aparticular region of salivary chromosome 2 have the following configurations (each letter denotes a band).(a) a b f e d c g h i j(b) a b c d e f g h i j(c) a b f e h g i d c j(d) a b f e h g c d i jAssuming that part (c) is the ancestral sequence, deduce the evolutionary ancestry of the other chromosomes.7.13 Two species of Australian grasshoppers coexist side by side. In meiosis, each has 8 pairs of chromosomes.When the species are crossed, the chromosomes in the hybrid form 6 pairs of chromosomes and one group of 4.What alteration in chromosomes structure could account for these results?7.14 Why are translocation heterozygotes semisterile? Why are translocation homozygotes fully fertile? If atranslocation homozygote is crossed with an individual that has normal chromosomes, what fraction of the F1 isexpected to be semisterile?7.15 Curly wings (Cy) is a dominant mutation in the second chromosome of Drosophila.
A Cy/+ male wasirradiated with x rays and crossed with +/+ females, and the Cy/+ sons were mated individually with +/+ females.From one cross, the progeny werecurly males146wildtype males0curly females0wildtype females163What abnormality in chromosome structure is the most likely explanation for these results? (Remember thatcrossing-over does not take place in male Drosophila.)7.16 Yellow body (y) is a recessive mutation near the tip of the X chromosome of Drosophila. A wildtype malewas irradiated with x rays and crossed with yy females, and one y+ son was observed. This male was mated with yyfemales, and the offspring wereyellow females256yellow males0wildtype females0wildtype males231The yellow females were found to be chromosomally normal, and the y+ males were found to breed in the samemanner as their father.
What type of chromosome abnormality could account for these results?7.17 In the homologous chromosomes shown here, the red region represents an inverted segment of chromosome.An individual of this genotype was crossed with an a b c d e homozygote. Most of the offspring were either A B CD E or a b c d e, but a few rare offspring were obtained that were A B c D E.
What events occurring in meiosis inthe inversion heterozygote can explain these rare progeny? Is the gene sequence in the rare progeny normal orinverted?Page 305Challenge Problems7.18 A wildtype strain of yeast, thought to be a normal haploid, was crossed with a different haploid strain carryingthe mutation his7. This mutation is located in chromosome 2 and is an allele of a gene normally required forsynthesis of the amino acid histidine. Among 15 tetrads analyzed from this cross, the following types ofsegregation were observed:4 wildtype : 0 his74 tetrads3 wildtype : 1 his74 tetrads2 wildtype : 2 his71 tetradHowever, when the same wildtype strain was crossed with haploid strains with recessive markers on otherchromosomes, segregation in the tetrads was always 2:2.
What type of chromosome abnormality in the wildtypestrain might account for the unusual segregation when the strain is mated with his7?7.19 A strain of semisterile maize heterozygous for a reciprocal translocation between chromosomes 1 and 2 wascrossed with chromosomally normal plants homozygous for the recessive mutations brachytic and fine-stripe onchromosome1.
When semisterile F1 plants were crossed with plants of the brachytic, fine-stripe parental strain, the followingphenotypes were found in a total of 682 F2 progeny.SemisterileFertilewildtype33319brachytic176fine-stripe1825273brachytic, fine-stripeWhat are the recombinant frequencies between brachytic and the translocation breakpoint and between fine-stripeand the translocation breakpoint?Further ReadingBickmore, W. A., and A. T. Sumner. 1989. Mammalian chromosome banding: An expression of genomeorganization. Trends in Genetics 5: 144.Carson, H. L.
1970. Chromosome tracers of the origin of the species. Science 168: 1414.Cavenee, W. K., and R. L. White. 1995. The genetic basis of cancer. Scientific American, March.Curtis, B. C., and D. R. Johnson. 1969. Hybrid wheat. Scientific American, May.Epstein, C. J. 1988. Mechanisms of the effects of aneuploidy in mammals. Annual Review of Genetics 22: 51.Guerrero, I. 1987. Proto-oncogenes in pattern formation. Trends in Genetics 3: 269.Hamel, P. A., B. L. Gallie, and R. A.
Phillips. 1992. The retinoblastoma protein and cell cycle regulation. Trendsin Genetics 8: 180.Hsu, T. H. 1979. Human and Mammalian Cytogenetics. New York: Springer-Verlag.Kamb, A. 1995. Cell-cycle regulators and cancer. Trends in Genetics 11: 136.Kimber, G., and M. Feldman. 1987. Wild Wheat: An Introduction. Columbia: University of Missouri Press.Manning, C. H., and H. O. Goodman. 1981. Parental origin of chromosomes in Down's syndrome. HumanGenetics 59: 101.Nathans, J.. 1989.
The genes for color vision. Scientific American, February.Richards, R. I., and G. R. Sutherland. 1992. Fragile X syndrome: The molecular picture comes into focus. Trendsin Genetics 8: 249.Stebbins, G. L. 1971. Chromosome Evolution in Higher Plants. Reading, MA: Addison-Wesley.Stewart, G. D., T. J. Hassold, and D.
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