UNIVERSITY OF KWAZULU-NATAL EXAMINATIONS: JUNE 2010 SUBJECT, COURSE AND CODE: GENE 240: Introductory Genetics DURATION: 3 HOURS TOTAL MARKS: 180 Internal Examiner: Dr M. Meusel External Examiner: Prof. P Watt PLEASE READ THE FOLLOWING INSTRUCTIONS CAREFULLY! 1 This paper consists of SECTION A (pages 2 to 7) and SECTIONS B, C and D (pages 7 to 10). Please check that your question paper is complete. 2 Read the questions carefully. 3 Number your answers exactly as the questions are numbered. 4 Use the total marks which can be awarded for each question as an indication of the amount of detail required. 5 It is in your own interest to write legibly and to present your work neatly. 6 SECTION A QUESTION 1 (a) AND (b) - MUST BE ANSWERED ON THE QUESTION PAPER. THE MULTIPLE CHOICE SECTION (1b) CARRIES A NEGATIVE MARKING FOR WRONG ANSWERS OF -0.25 MARKS. MAKE SURE TO HAND IN YOUR QUESTION PAPER WITH YOUR GREEN ANSWER BOOK! YOUR STUDENT NUMBER:... Section Total Student score Section A 1 20 Section A 2 40 Total Score 60
SECTION A: Definitions and Multiple Choice Questions University of KwaZulu-Natal Examinations, June 2010 Answer the questions from this section on this question paper and place it inside the Answer Book in which you answer Sections B-D. QUESTION 1 (a) On the space provided, write down the term(s) for the concept described. (10 x 2 marks) (1) A stage in which a synaptonemal complex begins to form. (2) A stage when sister chromatids separate from each other. (3) Alleles that produce independent effects when heterozygous. (4) A cross between parents differing in two traits (or two traits considered). (5) Gene that occurs with three or more allelic forms. (6) The percentage of individuals that show a particular phenotype among those capable of showing it. (7) Producing different type of reproductive cells with regard to the sex chromosomes. (8) A process that is the cause of abnormal numbers of chromosomes in gametes. (9) A chromosomal rearrangement that may change the position of the centromere. (10) A chromosome mapping technique that uncovers a recessive mutation. - 2 -
SECTION B : Short Answers (40 marks) Answer ALL the questions in this section in your Answer Book. QUESTION 2 a) Arrange the following randomly numbered events in the correct sequence as they occur in the cell. Write the correct sequence of numbers in your Answer Book. QUESTION 3 1 - Haploid cells are formed 2 - Synaptomal complex forms 3 - Chiasmata form 4 - Nuclear membrane and nucleolus disappear (first time) 5 - Segregation of alleles occurs 6 - Crossing over takes place 7 - Independent assortment is prepared 8 - Chromatid segregation takes place 9 - Membranes are formed around chromosomes with two sister chromatids 10 - Single kinetochores attach to spindle fibres Using the example of cystic fibrosis, explain how a trait can be identified as being dominant or recessive. Give five possible observations that can be made when studying human pedigrees, to support this identification. (5) (5) QUESTION 4 A mother with blood types A, Rh negative and N has a child with blood types O, Rh positive and MN. Indicate for each of the three blood typing systems an example of a phenotype that would exclude a male as being the potential father. Show all calculations/deductions. (6) QUESTION 5 a) Draw a Punnett square in which you show the genotypes and phenotypes of a dihybrid cross in which the two loci show duplicate gene action. (4) b) Using arrows, draw a simple flowchart that shows the general principle of the gene interaction, in a). (3) c) Indicate what phenotypic ratios are resulting from the gene action in a). (2) d) Give an example of a trait where the gene action in a) occurs in an organism. (1) - 3 -
QUESTION 6 a) Explain how sex is determined in animals with XX females and XO male. (3) b) How does sex determination work in Drosophila? (3) c) What does a ZW genotype indicate? (2) QUESTION 7 Using an example, briefly explain how genetic mosaics come about. (6) SECTION C: Problems (Show all calculations) [40] QUESTION 8 Two people, both heterozygous (Bb) for eye colour, marry and plan to have 7 children. What is the probability that: a) the fifth child will be a girl? b) the sixth child will have blue (bb) eyes? c) the seventh child will be a brown-eyed daughter? d) the couple will have 3 blue-eyed and 4 brown-eyed children? [10] QUESTION 9 A short-winged fly is crossed with a long-winged fly to give long-winged offspring. The long-winged offspring are crossed among themselves to produce 121 long-winged flies and 38 short-winged flies. State a null hypothesis to account for the observed frequencies, and perform a test to see whether the hypothesis is true. Would your conclusions change if you were to use a 1% confidence level? Explain your answer. (Table at the end of this Exam paper) [8] QUESTION 10 You sample a number of cells that have undergone meiosis. You find 137 cells with no crossovers, 63 with 1 crossover, 29 with 2 crossovers, 18 with three crossovers, and 4 with four or more crossovers between two known regions. What is the map distance between these two regions? [5] QUESTION 11 A heterozygous trihybrid corn plant is testcrossed and the following progeny are produced (all traits are recessive to their wildtype alternative): - 4 -
booster 6 booster, silkless 137 booster, liguleless, silkless 291 liguleless 142 liguleless, silkless 3 silkless 30 booster, liguleless 34 wildtype 339 a) What is the order of the loci on the chromosome? (3) b) Given the data above, what is the map distance between liguleless and silkless? (5) c) If we have a chromosome with three loci in which the distance between the loci is as indicated above, what is the probability of a double cross-over? (4) QUESTION 12 In a data set to determine crossover frequency between the sc, ec, and cv genes in Drosophila, the crossover frequency between ec and sc = 0.23, and between ec and cv = 0.31. The number of double crossover flies was 23 out of 500 flies. Calculate the Coefficient of Coincidence. (5) - 5 -
SECTION D: Answer the following two essay-type questions. Each essay should not be longer than 200 words. (Total 40 marks) QUESTION 13 Explain, how already in 1931 Creighton and McClintock could show that crossing over can indeed cause recombination of known genetic marker loci on chromosome 9 in maize. (20) QUESTION 14 Interpret the following figure. Make specific reference to the underlying reasons for the two different slopes visible in the curve. (20) Table for Question 9 PROBABILITY (CONFIDENCE LEVEL) DEGREES OF 0.95 0.90 0.80 0.70 0.50 0.30 0.20 0.10 0.05 0.01 0.001 FREEDOM 1 0.004 0/02 0.06 0.15 0.46 1.07 1.64 2.71 3.84 6.64 10.83 2 0.10 0.2 0.45 0.7 1.39 2.41 3.2 4.60 5.99 9.21 13.82 3 0.35 0.58 1.01 1.42 2.37 3.66 4.64 6.25 7.82 11.34 16.27 4 0.7 1.06 1.65 2.20 3.36 4.88 5.99 7.78 9.49 12.59 18.47-6 -