Hartl, Jones - Genetics. Principlers and analysis - 1998 (522927), страница 32
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The WhiteWyandotte breed is homozygous recessive for both genes cc ii. What proportion of the F2 progeny obtained frommating White Leghorn × White Wyandotte F1 hybrids would be expected to have colored feathers?2.22 The F2 progeny from a particular cross exhibit a modified dihybrid ratio of 9 : 7 (instead of 9 : 3 : 3 : 1). Whatphenotypic ratio would be expected from a testcross of the F1?2.23 Phenylketonuria is a recessive inborn error of metabolism of the amino acid phenylalanine that results insevere mental retardation of affected children.
The female II-3 (red circle) in the pedigree shown here is affected. Ifpersons III-1 and III-2 (they are first cousins) mate, what is the probability that their offspring will be affected?(Assume that persons II-1 and II-5 are homozygous for the normal allele.)2.24 Black hair in rabbits is determined by a dominant allele, B, and white hair by homozygosity for a recessiveallele, b. Two heterozygotes mate and produce a litter of three offpring.(a) What is the probability that the offspring are born in the order white-black-white? What is the probability thatthe offspring are born in either the order white-black-white or the order black-white-black?(b) What is the probability that exactly two of the three offspring will be white?2.25 Assuming equal sex ratios, what is the probability that a sibship of four children consists entirely of boys? Ofall boys or all girls? Of equal numbers of boys and girls?2.26 Andalusian fowls are colored black, splashed white (resulting from an uneven sprinkling of black pigmentthrough the feathers), or slate blue.
Black and splashed white are true breeding, and slate blue is a hybrid thatsegregates in the ratio 1 black : 2 slate blue : 1 splashed white. If a pair of blue Andalusians is mated and the henlays three eggs, what is the probability that the chicks hatched from these eggs will be one black, one blue, and onesplashed white?Challenge Problems2.27 In the mating Aa × Aa, what is the smallest number of offspring, n, for which the probability of at least one aaoffspring exceeds 95 percent?2.28 From the F2 generation of a cross between mouse genotypes AA × aa, one male progeny of genotype A— waschosen and mated with an aa female.
All of the progeny in the resulting litter were A—. From this result you wouldlike to conclude that the sire's genotype is AA. How much confidence could you have in this conclusion for eachlitter size from 1 to 15? (In other words what is the probability that the sire's genotype is AA, given that the a prioriprobability is 1 3 and that a litter of n pups resulted in all A— progeny?)2.29 Meiotic drive is an unusual phenomenon in which two alleles do not show Mendelian segregation from theheterozygous genotype. Examples are known from mammals, insects, fungi, and other organisms.
The usualmechanism is one in which both types of gametes are formed, but one of them fails to function normally. Theexcess of the driving allele over the other can range from a small amount to nearly 100 percent. Suppose that D isan allele showing meiotic drive against its alternative allele d, and suppose that Dd heterozygotes producefunctional D-bearing and d-bearing gametes in the proportions 3/4 : 1/4. In the mating Dd × Dd,(a) What are the expected proportions of DD, Dd, and dd genotypes?(b) If D is dominant, what are the expected proportions of D— and dd phenotypes?(c) Among the D— phenotypes, what is the ratio of DD : Dd?(d) Answer parts (a) through (c), assuming that the meiotic drive takes place in only one sex.Page 79Further ReadingAshley, C.
T., and S. T. Warren. 1995. Trinucleotide repeat expansion and human disease. Annual Review ofGenetics 29: 703.Bowler, P. J. 1989. The Mendelian Revolution. Baltimore, MD: Johns Hopkins University Press.Carlson, E. A. 1987 . The Gene: A Critical History. 2d ed.
Philadelphia: Saunders.Dunn, L. C. 1965. A Short History of Genetics. New York: McGraw-Hill.Hartl, D. L., and V. Orel. 1992. What did Gregor Mendel think he discovered? Genetics 131: 245.Huntington's Disease Collaborative Research Group: M. E. MacDonald, C. M. Ambrose, M. P. Duyao, R. H.Myers, C. Lin, L. Srinidhi, G. Barnes, S. A. Taylor, M.
James, N. Groot, H. MacFarlane, B. Jenkins, M. A.Anderson, N. S. Wexler, J. F. Gusella; G. P. Bates, S. Baxendate, H. Hummerich, S. Kirby, M. North, S.Youngman, R. Mott, G. Zehetner, Z. Sedlacek, A. Poustka, A.-M. Frischauf, H. Lehrach; A. J. Buckler, D. Church,L. Doucette-Stamm, M. C. O'Donovan, L. Ribe-Ramirez, M. Shah, V. P. Stanton, S. A. Strobel, K. M.
Draths, J. L.Wales, P. Dervan, D. E. Housman; M. Altherr, R. Shiang, L. Thompson, T. Fielder, J. J. Wasmuth; D. Tagle, J.Valdes, L. Elmer, M. Allard, L. Castilla, M. Swaroop, K. Blanchard, F. S. Collins; R. Snell, T. Holloway, K.Gillespie, N. Datson, D. Shaw, P S. Harper.
1993. A novel gene containing a trinucleotide repeat that is expandedand unstable on Huntington's disease chromosomes. Cell 72: 971.Judson, H. F. 1996. The Eighth Day of Creation: The Makers of the Revolution in Biology. Cold Spring Harbor,NY: Cold Spring Harbor Laboratory Press.Mendel, G.
1866. Experiments in plant hybridization. (Translation.) In The Origins of Genetics: A Mendel SourceBook, ed. C. Stern and E. Sherwood. 1966. New York: Freeman.Olby, R. C. 1966. Origins of Mendelism. London: Constable.Orel, V. 1996. Gregor Mendel: The First Geneticist. Oxford, England: Oxford University Press.Orel, V., and D. L. Hartl.
1994. Controversies in the interpretation of Mendel's discovery. History and Philosophyof the Life Sciences 16: 423.Stern, C., and E. Sherwood. 1966. The Origins of Genetics: A Mendel Source Book. New York: Freeman.Sturtevant, A. H. 1965. A Short History of Genetics. New York: Harper & Row.Page 80The calico cat illustrates the phenomenon of codominance.
This female is heterozygous for anallele for black fur and for an allele for orange (also called ''yellow") fur. Some patches of fur areblack, whereas other patches are yellow. Because both alleles express their characteristicphenotype when heterozygous, they are considered codominant. Why the black and orange alleles areexpressed in alternate patches of cells, rather than in overlapping patches, is explained in Chapter 7.The white spots are caused by an allele of a different gene that prevents any color formation.Page 81Chapter 3—Genes and ChromosomesCHAPTER OUTLINE3-1 The Stability of Chromosome Complements3-2 Mitosis3-3 MeiosisThe First Meiotic Division: ReductionThe Second Meiotic Division: Equation3-4 Chromosomes and HeredityChromosomal Determination of SexX-linked InheritanceNondisjunction as Proof of the ChromosomeTheory of HereditySex Determination in Drosophila3-5 Probability in Prediction and Analysis of Genetic DataUsing the Binomial Distribution in GeneticsEvaluating the Fit of Observed Results toTheoretical ExpectationsThe Chi-square Method3-6 Are Mendel's Data Too Good to be True?Chapter SummaryKey TermsReview the BasicsGuide to Problem SolvingAnalysis and ApplicationsChallenge ProblemsFurther ReadingGeNETics on the webPRINCIPLES• Chromosomes in eukaryotic cells are usually present in pairs.• The chromosomes of each pair separate in meiosis, one going to each gamete.• In meiosis, the chromosomes of different pairs undergo independent assortment because nonhomologouschromosomes move independently.• In many animals, sex is determined by a special pair of chromosomes—the X and Y.• The "criss-cross" pattern of inheritance of X-linked genes is determined by the fact that a male receives his Xchromosome only from his mother and transmits it only to his daughters.• Irregularities in the inheritance of an X-linked gene in Drosophila gave experimental proof of the chromosomaltheory of heredity.• The progeny of genetic crosses follow the binomial probability formula.• The chi-square statistical test is used to determine how well observed genetic data agree with expectationsderived from a hypothesis.CONNECTIONSCONNECTION: Grasshopper, GrasshopperE.
Eleanor Carothers 1913The Mendelian ratio in relation to certain Orthopteran chromosomesCONNECTION: The White-Eyed MaleThomas Hunt Morgan 1910Sex limited inheritance in DrosophilaCONNECTION: The Case Against Mendel's GardenerRonald Aylmer Fisher 1936Has Mendel's work been rediscovered?Page 82Mendel's experiments made it clear that in heterozygous genotypes, neither allele is altered by the presence of theother. The hereditary units remain stable and unchanged in passing from one generation to the next. However, atthe time, the biological basis of the transmission of genes from one generation to the next was quite mysterious.Neither the role of the nucleus in reproduction nor the details of cell division had been discovered.
Once thesephenomena were understood, and when microscopy had improved enough that the chromosomes could be observedand were finally recognized as the carriers of the genes, new understanding came at a rapid pace. This chapterexamines both the relationship between chromosomes and genes and the mechanism of chromosome segregation incell division.3.1—The Stability of Chromosome ComplementsThe importance of the cell nucleus and its contents was suggested as early as the 1840s when Carl Nägeli observedthat in dividing cells, the nucleus divided first.
This was the same Nägeli who would later fail to understandMendel's discoveries. Nägeli also failed to see the importance of nuclear division when he discovered it. Heregarded the cells in which he saw nuclear division as aberrant. Nevertheless, by the 1870s it was realized thatnuclear division is a universal attribute of cell division.
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