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2005 - THE UNIVERSITY OF HONG KONG BACHELOR OF SCIENCE...

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Unformatted text preview: THE UNIVERSITY OF HONG KONG BACHELOR OF SCIENCE: FINAL EXAMINATION BOTANY/ZOOLOGY: BIOL1106 Genetics 21 May 2005 2:30 pm — 4:30 pm Candidates may use any self-contained, silent, battery-operated and pocket-sized calculator. The calculator should have numeral-display facilities only and should be used only for the purpose of calculation. It is the candidate's responsibility to ensure that his/her calculator operates satisfactorily. Candidates must record the name and type of their calculators on the front page of their examination scripts. Answer any FIVE questions. All questions carry equal marks. 1. In garden peas, tall stem (I) is dominant over short stem (1‘), green pods (G) are dominant over yellow pods (g), and smooth seeds (S) are dominant over wrinkled seeds (5). Suppose a homozygous short, green, wrinkled pea plant is crossed with a homozygous tall, yellow, smooth one. (a) What will be the appearance of the F1? (b) What will be the appearance of the F2? (0) What will be the appearance of the offspring of a cross of the F1 back to its short, green, wrinkled parent? 2. The flowers of four o’clock plants may be red, pink or white. Reds crossed to whites produced only pink offspring. When pink flowered plants were crossed they produced 113 red, 129 white, and 242 pink offspring. It is hypothesized that these colours are produced by a single-gene locus with codominant alleles. Is this hypothesis acceptable on the basis of a chi-square test? The probablllfles of exceedlng different chi—square values for degrees of freedom from I to 50 when the expected hypothesis is irue" Probabilities 4/ .95 .90 .70 .50. .30 ‘20 .10 .05 , .01 .001 1 .004 .016 .15. .46 1.07 1.64 . 2.171 3.84 6.64 10.83 2 .10 .21 .71 , 1.39 ' 2.41 3.22 4.61 5.99 9.21 13.82 3 .35 .58 1.42 2.37 3.67 4.64 6.25 7.82 ‘ 11.35 16.27 4 .71 1.06 220 3.36 4.88 ' 5.99 p 7.78, 9.49 ' 13.28 18.47 5 1.15' 1.61 3.00 4.35 6.06 7.29 9.24 11.07 15.09 20.52 6 1.64 2.20 3.83 5.35 7.23 8.56 10.65 12.59 16.81 22.46 7 2.17 2.83 4.67 6.35 8.38 9.80 512.02 14.07 18.48 24.32 8 2.73 3.49 5.53 7.34. 9.52 11.03 13.36 15.51 20.09 26.13 9 3.33 4.17 6.39. 8.341 10.66 12.24 14.68 16.92 - 21.67 27.88 10 3.94 4.87 7.27 9.34 11.78 13.44 15.99 18.31 23.21 29.59 11 4.58 . 5.58 8.15 10.34 ' 12.90 14.63 17.28 19.68 24.73 31.26 72 5.23 6.30 9.03 1 1.34 14.01 15.81 18.55 21.03 26.22 32.91 1.1 5.89 7.04 9.93 12.34 15.12 16.99 19.81 22.36 27.69 34.53 14 6.57 7.79 10.82 13.34 16.22 18.15 21.06 23.69 29.14 36.12 15- . 7.26 8.55 1 1.72 14.34 17.32 19.31 22.31 25.00 30.58 37.70 20 10.85 12.44 16.27 19.34 22.78 25.04 28.41 31.41 37.57 45.32 25 14.61 16.47 20.87 24.34" 28.17 30.68 34.38 37.65 44.31 52.62 30 18.49 20.60 25.51 29.34 33.53 36.25 g 40.26 43.77 _ 50.89 59.70 50 34.76 37.69 44.31 49.34 54.72 58.16 63.17 67.51 76.15 86.66 410516041 ' Abridgld from Table IV of Fisher and Yatu, Statistical Table: for dialogkol, Agricultural and Medical Research, Oliver and Boyd Lint, Edinburgh, by ”mission- of the authors and publlihers. 1/2 Discuss the changes in the gene’s definition from Mendel’s time to now. Discuss the possible causes of genetic variation at the cellular and molecular levels. (a) Describe the unique features of the DNA molecule; (b) Describe the historical aspect of genome sequencing. You have sampled a population and determined that it has two alleles (A1 and A2) at a locus. Of the individuals you sampled, 500 are homozygous for A1, 200 are heterozygous, and 300 are homozygous for A2. The population may or may not be in Hardy-Weinberg equilibrium. (a) What is the frequency of AlAl homozygotes? (b) What is the value of p, the frequency of A1? (c) What is the frequency of the A2A2 homozygotes if the population were in Hardy-Weinberg equilibrium? (d) What is the observed heterozygosity at the locus? (o) Is this population in Hardy~Weinberg equilibrium? Can you answer the question without performing the chi-square test? Explain. (f) Describe the mathematical relationships among the variables in the Hardy-Weinberg equations, and explain the conditions or assumptions under which those relationships hold. The neutral theory of molecular evolution holds that the vast majority of nucleotide substitutions are selectively neutral; random genetic drift therefore dominates evolution at the DNA level. Which of the following lines of evidence support(s) or contradict(s) this theory? (3.) Amino acid sequences of many proteins appear to change steadily over time (in more or less a "clocklike" fashion), as do many DNA sequences; (b) Synonymous or silent-site substitution rates are higher than nonsynonymous (replacement) substitution rates; (0) Pseudogenes consistently have the highest divergence rates of DNA sequences studied; and (d) Codon bias. Explain your answer. - END OF PAPER - 2/2 ...
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