Biology 2C03 Term Test #3

Transcription

1 Biology 2C03 Term Test #3 Instructors: Dr. Kimberley Dej, Ray Procwat Date: Monday March 22, 2010 Time: 10:30 am to 11:20 am Instructions: 1) This midterm test consists of 9 pages. Please ensure that all pages are present. 2) Print your name and student number at the top of each page. Also, print your name and student number on the scantron card. 3) There are 20 multiple-choice questions (1 mark each). Please use the computer card to record your multiple-choice answers. Any answers not indicated on the scantron card will not be graded. (20 marks total) 4) There are 2 short-answer questions. Please answer these questions in the allotted space on this quiz. (15 marks total). 5) The final grade is out of 35 marks. 6) The test is 50 minutes long. 7) Please hand in the test package and the scantron card at the end of the test. Removal of tests is considered academic dishonesty. Good luck!! Grade: MCQ : /20 SA: /15 Final: /35 Biology 2CO3: Genetics Winter 2010 Page 1 of 9

2 Part A. 20 Multiple-choice questions: 1 mark each. Please indicate your answers on the scantron card. Questions 1 to 4. A black female cat (XbXb) and an orange male cat (XBY) were mated to each other and produced a male cat that was calico. 1. What is the karyotype and genoytype of this cat with respect to the sex chromosomes only? a) XbXBXB b) XbYB c) XbXBXb d) XbXBY e) Xb 2. How many Barr Bodies would you see in this cat s somatic cells? a) none b) one c) two d) three e) four 3. Which sex chromosomes and genotypes did this male inherit from his father? (1 mark) a) Xb b) XbY c) XBY d) YB e) XB 4. Male calico cats are rare. What mistake caused this to occur, when did it occur and in which parent? a) Nondisjunction in meiosis I of the mother b) Nondisjunction in meiosis II of the father c) Nondisjunction in meiosis I of the father d) Nondisjunction in meiosis II of the father e) More than one of these above options is possible 5. What is the product of the Xist locus that is required for X-inactivation? a) a protein that coats the active X-chromosome b) a protein that coats the inactive X-chromosome c) an RNA that coats the active X-chromosome d) an RNA that coats the inactive X-chromosome e) the product has not yet been characterized Biology 2CO3: Genetics Winter 2010 Page 2 of 9

3 6. In the following diagram, which is an example of a cis-acting sequence and which is an example of a trans-acting factor? a) b) c) d) e) cis-acting enhancer activator TFIID silencer activator trans-acting silencer TFIID promoter activator enhancer 7. Gene silencing (preventing gene transcription): a) involves changes in nucleotide sequence, C to G b) may occur through the methylation of cytosines c) may occur by histone acetylation in heterochromatin d) involves gene splicing e) both a and b 8. Which is an example of post-transcriptional processing that occurs during the synthesis of a mature eukaryotic mrna a) removal of intervening sequences (introns) b) DNA methylation c) chromatin remodeling d) histone acetylation 9. What would be the genotype of the four gametes produced by nondisjunction of the X chromosomes at the second division in the formation of a spermatocyte in humans (note: nullo means a gamete with no sex chromosomes). a) X, X, Y, Y b) XY, XY, nullo, nullo c) Y, Y, nullo nullo d) X, X, YY, nullo e) XX, Y, Y, nullo Biology 2CO3: Genetics Winter 2010 Page 3 of 9

4 Questions 10 to 13. You are given the following diagram of an imprinted region of the human genome (maternally inherited chromosome is shown). H19 is transcribed from the maternal chromosome, but Igf2 is not. In contrast Igf2 is transcribed from the paternally inherited chromosome, but H19 is not. In the paternally inherited chromosome, but not in the maternally inherited one, DNA methylation in detected immediately upstream, 5 from the start of transcription of the H19 gene. This phenomenon is known as genomic imprinting. Maternally inherited chromosome 10. What is the name of the cis regulatory DNA sequence that prevents activation of the gene Igf2 on the maternal chromosome? a) inhibitor b) activator c) methylation-sensititive site d) enhancer e) insulator 11. What do you expect to see with respect to expression of Igf2 and H19 alleles located in the maternal chromosome if there was a loss of function mutation in the gene encoding the CTCF protein? a) Both Igf2 and H19 active b) Both Igf2 and H19 inactive c) Igf2 active and H19 inactive d) Igf2 inactive and H19 active 12. What do you expect to see with respect to expression of the paternal chromosome if there was a loss of function mutation in the CTCF gene? a) Igf2 and H19 active b) both Igf2 and H19 inactive c) Igf2 active and H19 inactive d) Igf2 inactive and H19 active 13. What would be the effect on transcription of the maternal and paternal chromosomes of an inability to methylate DNA at the start of transcription of the H19 gene? a) there would be no effect on either chromosome b) maternal chromosome transcription of H19 gene but not of IGF2 gene would change c) paternal chromosome transcription of the H19 gene only would change d) both transcription of both maternally and paternally inherited genes would change Biology 2CO3: Genetics Winter 2010 Page 4 of 9

5 Questions 14 to 17. Prader-Willi syndrome is associated with a mutation in the gene SNRPN. The chromosomal region containing the SNRPN gene is may be genomically imprinted. Below is a pedigree showing the pattern of inheritance of this trait. 14. If a mother carries the mutation and passes it on to her son, will he be affected? a) Yes, 100% chance b) No, 0% chance c) 50% chance of being affected 15. If a father carries the mutation and passes it on to his daughter, will she be affected? a) Yes, 100% chance b) No,0% chance c) 50% chance of being affected 16. If a father carries the mutation, but does not express the phenotype, and passes the mutation on to his son, will his grandchildren be affected? a) Yes, for each there is a 100% chance of being affected b) Yes, for each there is a 50% chance of being affected c) No, there is no chance of being affected 17. This is likely an example of: a) X-inactivation b) maternal imprinting to inactivate the SNRPN gene c) paternal imprinting to inactivate the SNRPN gene Biology 2CO3: Genetics Winter 2010 Page 5 of 9

6 Questions 18 to 20. A woman is asymptomatic for hemophilia and colourblindness, but her father was affected by both. The distance between these two genes on the X-chromosomes in humans is 10 centimorgans. 18. What is the probability that this woman's son will be affected by hemophilia? a) 0% b) 25% c) 50% d) 75% e) 100% 19. What is the probability that this woman's son will be affected by both hemophilia and colourblindness? a) 5% b) 10% c) 22.5% d) 45% e) 50% 20. This woman has a son who is affected by hemophilia. What is the probability that he is not affected by colourblindness? a) 5% b) 10% c) 45% d) 50% e) 90% Biology 2CO3: Genetics Winter 2010 Page 6 of 9

7 Part B. Short answer questions: 25 marks total Please write your answers in the spaces provided. 1. (Total: 8 marks) The following diagram was used in class to represent bivalents that may tend to lead to nondisjunction in females. (a) Which image (A or B) represents the more unstable bivalent? (1 mark) B (b) At which stage does meiosis normally arrest or stall in human females and for how long? (2 marks) Prophase I, from fetus to ovulation perhaps 14 to >40 years (c) What is holding together the homologues in the above images? (2 marks) Crossovers and sister chromatid cohesion (cohesin proteins) (e) Explain a simple model for what may lead to nondisjunction in human females as they get older. (1 mark) Premature loss of cohesion proteins in meiosis I (g) Human monosomies are commonly lethal. Name one exception to this and explain why it is an exception. (2 marks) XO (Turner's syndrome) One X chromosome is much like two X chromosomes if one is inactivated by dosage compensation Biology 2CO3: Genetics Winter 2010 Page 7 of 9

8 2. You are given the following linkage map of Drosophila melanogaster: Biology 2CO3: Genetics Winter 2010 Page 8 of 9

9 Question 2: FIGURE TO LEFT (Total: 7 marks) (a) Draw the cross needed to find the distance between the following genes (indicate the male and the female parents in the cross). (i) hairless bristles and Delta veins on chromosome 3 (in coupling) H D/h d female x h d /h d male (b) vermillion eyes and miniature wings on the X chromosome (in repulsion) V m/v M x v m/y (c) What is the value for the amount of recombination that you would see for a dihybrid cross between the following two genes (i)) Sable body and Bar eyes (on the X chromosome) 14 m.u. (ii) Rough eyes and claret eyes (on chromosome 3) 9.6 m.u. (iii) star eyes and plexus wings (on chromosome 2) genes are far apart and would only show 50% recombination (iv) eyeless and curved wings (on the 4th and 3rd chromosomes, respectively) these genes are on different chromosomes and would show 50% recombination (v) What is the value of interference if you see 2 double recombinants out of 1000 flies when studying the genes held-out wings and clot eyes on chromosome 2. coc = obs/exp = 2 / (9%)(3.5%)1000 flies = 2/3.15 = 63% Interference = 1- coc = 37% This is the end of the test. Biology 2CO3: Genetics Winter 2010 Page 9 of 9