Biological Sciences 50 Practice Exam 1

Transcription

1 NAME: Fall 2005 TF: Biological Sciences 50 Practice Exam 1 A. Write your name on each page. B. Write your answer on the same page as the question. THE SPACE PROVIDED IS MEANT TO BE SUFFICIENT; BE BRIEF, BE CAREFUL, BE CONCISE! If absolutely necessary, use the back of that page to continue the answer. C. IF YOUR ANSWER CANNOT BE READ IT CANNOT BE GRADED!!! D. Remember, if you do not show all your work, you cannot get partial credit. E. The point value for each question is noted. Allocate your time wisely. F. Read carefully, think before you write, good luck, and do well! IF YOU WRITE IN PENCIL, YOU CANNOT ASK FOR A REGRADE! Question 1: Question 2: Question 3: Question 4: Question 5: Question 6: (10 pts) (10 pts) (20 pts) (24 pts) (24 pts) (12 pts) TOTAL: (100 pts)

2 Name Page 2 of 8 Short answer (5 2 pts each) 1a) For the genotypes AA, Aa and aa, what cross yields all Aa progeny? b) For the genotypes AA, Aa and aa, what cross yields AA, Aa and aa progeny? c) : : In Problem 2, what is the ratio of AA : Aa : aa progeny? d) An individual of genotype AA Bb Cc DD Ee is testcrossed. Assuming that the loci undergo independent assortment, what fraction of the progeny are expected to have the genotype Aa Bb Cc Dd Ee? e) Stage of mitosis or meiosis in which chromosomes oriented on opposite sides of the metaphase plate undergo separation. 2. (10 points) There is a strain of D. melanogaster that is pure-breeding for white eyes and another strain that is pure-breeding for red eyes. When white-eyed females are crossed to redeyed males, the progeny are red-eyed females and white-eyed males. a) Explain this result. Give the genotypes of the parents and progeny and define all symbols used.

3 Name Page 3 of 8 3. (20 points) Type 1 albinism in humans is a rare hereditary condition associated with a reduced amount of tryosinase, an enzyme required for the conversion of the amino acid tyrosine to the dark pigment melanin. In the following pedigree, males are indicated by squares, females by circles and individuals with type 1 albinism are indicated by shading. A B C D E a) What is the mode of inheritance of type 1 albinism? Explain your reasoning.

4 Name Page 4 of 8 b) List the genotypes of the indicated family members as specifically as possible with the data available. If there is more than one possibility, clearly indicate all possibilities. Except where necessary to explain the pedigree, assume that the individuals marrying into the family are homozygous wild-type. Individual A Individual B Individual C Individual D Individual E c) If individuals B and E marry, what is the probability that their first child will be affected by type 1 albinism? Show your work. d) If their first child is affected, what is the probability that their second child will be unaffected? Show your work.

5 Name Page 5 of 8 4. (24 points) Female Drosophila melanogaster heterozygous for three recessive alleles a, b, and c are crossed to abc males. The phenotypes of 10,000 progeny are scored as follows: abc bc 750 a b+ 230 a+c c 8 ab+ 12 a) What results would you expect if a, b, and c were unlinked? b) Based on the observed results, what is the map order? Explain your reasoning.

6 Name Page 6 of 8 c) Using all of the relevant data, calculate each of the three two-factor recombination frequencies. Show your work. Express all frequencies as percentages. d) What is the frequency of double recombination? Show your work. f) What frequency of double recombination would you calculate if the data contained no evidence of interference? Show your work

7 Name Page 7 of 8 5. (24 pts) Use the diagram of the DNA replication fork below to answer the following questions. A) Assume the direction of replication is right to left. Draw and label the leading and lagging strands on this diagram. Be sure to label the 5 and 3 ends of both strands. B) Indicate where helicase would be found and its direction of movement. C) Indicate the one or more sites where DNA polymerase would be found and its/their direction of movement. D) Indicate with a yes/no answer whether the following situations interfere with the replication process diagrammed above: 5 Affects leading strand Affects lagging strand i) the presence of dideoxy-thymidine: ii) absence of functional ligase: iii) defective spliceosome machinery: iv) absence of functional telomerase: E) The base sequence of a region where DNA replication begins is shown below. What is the sequence of the primer that is synthesized complementary to the bases in bold? Be sure to indicate the 5 and 3 ends. 5 - A G G C C T C G A A T T C G T A T A G C T T T C A G A A -3

8 Name Page 8 of 8 6. (12 points). a. If you place a culture of eukaryotic cells into medium containing 3 H-thymine just prior to S, how will this radioactivity be distributed in a pair of homologous chromosomes at metaphase? Would the radioactivity be in (a) one chromatid of one homolog, (b) both chromatids of one homolog, (c) one chromatid each of both homologs, (d) both chromatids of both homologs, or (e) some other pattern? Choose the correct answer and explain your reasoning. b. If these same cells are then allowed to go through a second S phase but with only nonradioactive nucleotides available, how would you expect the radioactivity to now be distributed in a pair of homologous chromosomes at metaphase? (Ignore the effect recombination might have on this outcome.) Would the radioactivity be in (a) one chromatid of one homolog, (b) both chromatids of one homolog, (c) one chromatid each of both homologs, (d) both chromatids of both homologs, or (e) some other pattern? Choose the correct answer and explain your reasoning. Optional (check one answer for each question) This exam was too short too long about right This exam was too easy too hard about right Write brief additional comments about the exam (or the course so far) below: