MBG*2040 Foundations in Molecular Biology and Genetics Mock Midterm Exam Winter 2012 It is most beneficial to you to write this mock midterm UNDER EXAM CONDITIONS. This means: • Complete the midterm in an hour and 15 minutes. • Work on your own. • Keep your notes, textbook, and workbook closed. • Attempt every question. After the time limit, go back over your work with a different colour or on a separate piece of paper and try to do the questions you are unsure of. Record your ideas in the margins to remind yourself of what you were thinking when you take it up during session. The purpose of this mock midterm is to give you practice answering questions in a timed setting and to help you to gauge which aspects of the course content you know well and which are in need of further development and review. Use this mock midterm as a learning tool in preparing for the actual midterm. Please be advised that we do not have previous knowledge about the content of your midterm, so do not focus your studying simply on the material presented in the mock exam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his version of the mock midterm will be reviewed and discussed during the following SLG sessions: Date and Time Location Leader Tues/Thurs LIB 120A Leah 11:30-1 pm Thursday LIB 384 Levy 5:30-8:30pm The following Scenario applies to questions 1-4 Gaucher Disease Type I Gaucher Disease Type I (GD-I) is a rare single gene disorder which is fully penetrant. Affected individuals have enlarged livers and spleens, bone abnormalities, and anaemia. GD-I is caused by a defect in the gene that encodes the enzyme glucocerebrosidase. The gene maps to chromosome 1. Glucocerebrosidase functions in the lysosome to degrade certain complex lipids (glucocerebrosides). If the enzyme functions poorly then partially degraded lipids accumulate in the lysosomes of cells. The macrophages of the immune system are particularly sensitive to this process and lipid-laden macrophages accumulate in the bone marrow where they compromise the production of red blood cells and platelets. The pedigree below represents a hypothetical family affected with GD-I. Shaded symbols represent individuals affected with GD-I and open symbols represent phenotypically normal individuals. The following four questions refer to this information. 1. Individual III-2 marries individual III-6. What is the probability that the first child of these parents will be affected with GD-I? a) 1/8 b) 1/12 c) 1/18 d) 1/64 e) none of the above 2. Individual III-8 marries individual III-3. What is the probability that their first child will be a carrier of GD-I? a) ! b) 1/6 c) 1/8 d) 1/12 e) none of the above Read over the following statements. i) There are a number of inherited diseases that are phenotypically similar to GD-I and each is usually associated with one of the genes that encodes a lysosomal enzyme. For example, Wolman Disease is caused by mutations in a gene found on chromosome 10 and Nieman-Pick Disease is caused by mutations in a gene found on chromosome 11. Both of these diseases are phenotypically similar to GD. ii) Individuals infected with certain viruses can show symptoms similar to GD-I. iii) Researchers have identified several forms of Gaucher Disease that are due to different mutations in the single gene encoding glucocerebrosidase. Patients with Gaucher Disease Type I are often homozygous for certain alleles which result in the production of an altered enzyme. Individuals with Gaucher Type II are homozygous for null alleles and have severe symptoms which typically cause death before the age of 5. Gaucher Disease Type III is associated with milder symptoms and adult onset. Type III patients can be homozygous for certain alleles that result in the production of reduced amounts of the enzyme. 3. The above statements illustrate which of the following phenomena? a) i) variable expressivity; ii) pleiotropy; iii) incomplete penetrance b) i) allelic heterogeneity; ii) phenocopy effect; iii) locus heterogeneity c) i) variable expressivity; ii) phenocopy effect; iii) locus heterogeneity d) i) locus heterogeneity; ii) phenocopy effect; iii) allelic heterogeneity e) none of the above 4. The blood and tissues of two individuals affected with Gaucher Disease were examined. In Patient A, no evidence of the enzyme glucocerebrosidase could be found. In Patient B, the enzyme was found in normal quantities but the enzyme was non-functional. What is a good explanation for these observations? a) In Patient A, the glucocerebrosidase gene was not transcribed due to a mutation in the regulatory region. b) In Patient B, the glucocerebrosidase gene was transcribed but the mRNA was not translated. c) In Patient B, there could be large deletion in the regulatory region of the glucocerebrosidase gene and the protein encoding region of the glucocerebrosidase gene is normal. d) Patient A could be homozygous for recessive hypermorphic allele of the glucocerebrosidase gene. e) More than one of the above is possible. 5. A tetrahybrid plant (AaBbCcDd) is crossed to a plant with the genotype AAbbCcdd. All genes show simple dominance and are independently assorting. What percentage of progeny will show the same phenotype as the tetrahybrid parent? a) More than 30% b) Between 20% and 30% c) Between 10% and 20% d) Between 1% and 10% e) Less than 1% Coat texture in dogs is controlled by gene W. Wire hair is dominant over smooth hair. Hair colour is controlled by the gene B. Black hair is dominant over brown hair. A third gene controls ear carriage. Dogs with the dominant allele, H, have lop ears and dogs that are homozygous recessive have erect ears. A trihybrid female dog is crossed to a trihybrid male dog. All genes are independently assorting and show simple/complete dominance. 6. A wire-haired, black, lop-eared puppy is produced from the above cross. What is the probability that this puppy is a trihybrid? a) 1/8 b) 1/16 c) 4/27 d) 6/27 e) none of the above 7. Gene W has two alleles. One allele of gene W is completely dominant to the other allele. Gene W is expressed only in males. Gene A has two alleles with one being incompletely dominant to the other allele. Gene W and Gene A are autosomal and independently assorting. A dihybrid female is crossed to a dihybrid male. Which of the following statements describes their offspring? a) 3 different phenotypes would be observed in male offspring and 2 different phenotypes would be observed in female offspring. b) 12 different phenotypes would be observed in male offspring and 6 different phenotypes would be observed in female offspring. c) 6 different phenotypes would be observed in male offspring and 3 different phenotypes would be observed in female offspring. d) 6 different phenotypes would be observed in male offspring and 2 different phenotypes would be observed in female offspring. e) 6 different phenotypes would be observed in male offspring and 6 different phenotypes would be observed in female offspring. The following Scenario applies to question 8 In summer squash, the allele for yellow fruit colour, w, is recessive to the allele, W for white fruit colour. The allele for disc-shaped fruits, S, is dominant to the allele, s, which results in sphere- shaped fruit. Both genes are autosomal. True-breeding plants which produce yellow, disc- shaped fruits were crossed to true-breeding plants which produce white, sphere shaped fruits. The resulting F1 progeny were intercrossed. The following F2 progeny were produced: 8. The expected number of F2 plants producing white and disc-shaped fruits, if the genes were independently assorting, is a) 500 b) 1500 c) 2000 d) 4500 e) none of the above 9. What is/are the genotype(s) of the above dihybrid parents? a) SW//sW b) SW//Sw c) SW//sw d) sW//Sw e) More than one of the above 10. A trihybrid plant GgHhWw is test-crossed. If genes G, H, and W are very tightly-linked (do not recombine), how many phenotypic classes of progeny will there be? a) 4 b) 8 c) 2 d) 6 e) 1 11. Calico or Tortoiseshell cats a) Have skin cells with Barr bodies. All other somatic cells are normal and lack Barr bodies. b) Are dihybrid females with yellow and black patches of fur. c) Are usually females that are mosaics for two autosomal coal colour alleles. d) Are usually females that are heterozygous for two sex-influenced coat colour genes. e) Are heterozygous for one X-linked coat colour gene. 12. Nail-patella Syndrome is caused by a rare dominant allele, N. This locus is 20 map units from the ABO blood type locus. Note: shaded individuals are affected with Nailpatella Syndrome. The letters below the pedigree symbols indicate the individual's blood type. What is the probability that the first child of II-1 and II-2 will have Type B blood with Nail-patella Syndrome? a) 0.2 b) 0.1 c) 0.25 d) 0.4 e) none of the above 13. A rare autosomal dominant sex-limited gene is known to cause premature greying in men but is without effect in women. A man with premature greying has type A blood. His wife has type B blood and her family history shows no evidence of premature greying. Their first child has type O blood. What is the probability that their next child will be a male with type A blood, who will develop premature greying? a) " b) 1/16 c) 1/8 d) ! e) 0 14. The following statements refer to meiosis and mitosis in humans. i. Non-identical sister chromatids separate during Anaphase II of meiosis. ii. 23 bivalents form during prophase II of meiosis iii. The first polar body contains the same number of chromatids as the secondary oocyte. iv. In prophase I of meiosis there are 46 chromosomes (consisting of 2 chromatids each) and in prophase II of meiosis there are 23 chromosomes (consisting of 1 chromatid each). v. Females are born with their primary oocytes arrested in prophase of mitosis. Of the above statements, how many are correct? a) 5 b) 4 c) 3 d) 2 e) 1 15. A sex-linked gene, S, controls feather colour in chickens. Birds with the dominant allele, S, have silver feathers and birds homozygous or hemizygous for the recessive allele, s, have gold feathers. A gold-coloured male is bred to a silver-coloured female. A single male offspring is produced from this cross. What is the probability that this male offspring have silver feathers? a) 1 b) ! c) 1/2 d) 0 e) none of the above 16. Three breeds of rex cat are: Cornish Rex, Devon rex, and German Rex. In each breed, the rex trait appears to be autosomal recessive. Breeders are wondering whether the rex trait is controlled by three different genes or three different alleles of the same gene. True breeding cats were crossed and the results were: True Breeding Cross F1 Offspring Parents A Devon x Cornish All normal B Devon x German All normal C Cornish x German All rex What can be concluded from the table? a) Cornish and Devon phenotypes are controlled by different alleles of one gene b) German and Devon phenotypes are controlled by different alleles of one gene c) Cornish and German phenotypes are controlled by different alleles of one gene d) Cornish and German phenotypes are controlled by 2 genes e) Cornish, Devon, and German phenotypes are controlled by different alleles of one gene f) Cornish, Devon, and German phenotypes are controlled by 3 genes g) None of the above 17. One chromosome at metaphase of mitosis typically consists of a) 4 non-identical DNA molecules b) 2 non-identical DNA molecules c) 1 very long DNA molecule d) 2 identical DNA molecules e) None of the above 18. In cats, three alleles (C, cb, and cs) at an autosomal locus control the amount of pigment in the coat. The various allele combinations and the resultant phenotypes are shown in the following table. From the above table, it can be concluded that the cb allele a) is incompletely dominant to the cs allele b) is recessive to the C allele but is completely dominant to the cs allele c) is epistatis to the cs allele, but not to the C allele d) is recessive to both the C and the cs allele e) more than one of the above is correct 19. The turnip is 2N = 20. How many bivalents and chromatids are present in Prophase I of meiosis in turnip cells? a) 10 and 20 respectively b) 10 and 40 respectively c) 0 and 20 respectively d) 0 and 40 respectively e) None of the above 20. Streaked hairlessness is an autosomal dominant trait in cattle. Affected animals lack hair in vertical streaks over the hips and sides. The dominant allele is lethal in the homozygous condition. The absence of horns (the polled condition) in cattle is caused by a single autosomal gene which is dominant in females and recessive in males. A polled, hairless male is crossed to a horned, hairless female. The viable female progeny will be hairless male is crossed to a horned, hairless female. The viable female progeny will be a) " polled and hairless; " polled with normal hair b) # horned and hairless; ! polled with normal hair c) 2/3 polled and hairless; 1/3 polled with normal hair d) 2/3 horned and hairless; 1/3 horned with normal hair e) none of the above 21. Treacher-Collins Syndrome (TCS) is a very rare autosomal dominant trait which shows a penetrance of 60%. Affected individuals show facial abnormalities. A woman with TCS marries a phenotypically normal man with no family history of TCS. What is the probability that their first child will show TCS facial abnormalities? a) 30% b) 37.5% c) 50% d) 20% e) none of the above Alpha-1-antitrypsin (AAT) is a protease inhibitor, deficiency of which is associated with emphysema and liver disease. In normal individuals, AAT protects the lungs from an enzyme called elastase. Elastase digests damaged or aging lung cells and bacteria and aids in the healing process. However, excess elastase can attack healthy human lung tissue. AAT, in sufficient amounts, traps and destroys elastase before it has a chance to damage lung tissue. 22. In a region of the United States, approximately 3% of the population are carriers of a mutant AAT allele. Two phenotypically normal people from this population marry. What is the approximate probability that their first child will be affected with AAT deficiency? a) 25% b) 0.75% c) 2% d) 0.02% e) none of the above 23. An Andalusian chicken breeder has birds with black feathers, blue feathers, and white feathers. She makes a number of crosses and produces the following table: What statements are consistent with the results shown in the table? a) Chickens with blue plumage do not breed true b) Three alleles of one gene control feather colour c) The blue allele is completely dominant to the white allele d) Blue chickens must be heterozygous for two feather colour genes e) More than one of the above is true Questions 24 to 26 are true/false questions. 24. According to Gregor Mendel’s First Law, the two alleles of a gene are always distributed into separate gametes. a) The above statement is true b) the above statement is false 25. All of the cytoplasm and mitochondrial DNA (mtDNA) in a zygote are maternal a) The above statement is true b) the above statement is false 26. The gene/s that determine femaleness in Drosophila are primarily located on the autosomes. a) The above statement is true b) the above statement is false 27. A male with classic X-linked haemophillia was found to have a transposable element inserted in the middle of the blood clotting factor VIII gene. We want to determine if one of his mother’s X chromosomes also contained this specific transposable element. If so, the mother would be heterozygous and would have 50% chance of passing the chromosome containing the transposable element to her children. However, it was discovered that this transposable element was not found on either of her X chromosomes! It was on chromosome 22. What is most likely to be true? a) Her son could have inherited his mother’s chromosome 22 with the transposable element. In the germ-line cells of the son, it could have moved to the X chromosome. b) The transposable element could have moved to the X chromosome in the gamete-forming cells of the mother prior to being transmitted to her son. c) Her son could have inherited his mother’s chromosome 22 with the transposable element. Shortly after birth, it could have moved to the X chromosome. d) None of the above. EXTRA PRACTICE! 28. The following is a pedigree from a cat breeder. Hairlessness (a rare trait) is indicated by solid symbols. Cats with hair are indicated by open symbols. What is the probability that: a) A mating between III-1and III-2 will produce a cat with no hair? b) A mating between II-1 and III-1 will produce a cat with no hair? c) A mating between III-1 and III-2 will produce a normal cat that is carrier for no hair?
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