1 GENETICS – BIO325 Spring 2014 Prof: Janice Fischer EXAM #1 (Learning Objectives in Classes 1-3) January 28, 2014 Name _____Answer Key____________________________ • No questions will be answered during the exam. Figuring out what the questions mean is part of the exam. • Read the questions carefully. You need to answer my questions, not different ones that you like better. • If your answer is an equation, it is OK to leave it in that form. If you solve it and make an arithmetic error you will have the wrong answer and get no credit. • CIRCLE EVERY SINGLE ANSWER THAT YOU WANT GRADED. IF NOTHING IS CIRCLED or MORE THAN ONE ANSWER IS CIRCLED, YOU WILL GET NO CREDIT. The reason for this is that you cannot write down a variety of answers and expect me to choose the right one from among them, or to give you partial credit if the right answer is among them. The numbers in parentheses next to each question indicate the points, out of 100, that the question is worth.2 1. The following DNA sequence of part of the template strand of a gene: 5’-GGGTACGTACCCGGG-3’ A. (5 pts) Write the sequence of the corresponding transcript – be sure to indicate the 5’ end. 5’-CCCGGGUACGUACCC-3’ B. (5 pts) Write the sequence of the non-template DNA strand – be sure to indicate the 5’ end. 5’-CCCGGGTACGTACCC-3’ C. (5 pts) The part of the transcript shown is in the middle of an open reading frame; the codons are read starting with the first base at the 5’ end of the mRNA fragment you indicated in part (A) above. Write the polypeptide sequence encoded by this part of the mRNA. Use 3-letter abbreviations for amino acids, and be sure to indicate the N terminus and C terminus. 5’-CCC GGG UAC GUA CCC -3’ N- Pro – Gly – Tyr– Val – Pro -C 2. (15 pts) Use the line below to diagram the parts of a human mRNA that is processed and ready to be translated. Your diagram should indicate the locations of the following components: A. 5’methyl-G cap B. poly-A tail C. open reading frame D. exons E. introns F. start codon (AUG) G. stop codon (i.e. UAG) H. 5’ UTR I. 3’ UTR ABE- not present in processed mRNAF GCHID3 3. The F1 in Mendel’s dihybrid cross were heterozygous for dominant and recessive alleles of two different genes (Aa Bb). A. (5 pts) How many different gamete types did the F1 produce? FOUR B. (5 pts) Write the genotype of each gamete produced by the F1. AB, Ab, aB, ab C. (10 pts) What fraction of the F2 (produced by selfing the F1) were AA Bb ? 1/4 (AA) X 1/2 (Bb) = 1/8 4. (5 pts) You roll two dice. What is the probability that the sum of the numbers on both dice will be 5? (1 + 4) or (2 + 3) or (3 + 2) or (4 + 1) 1/36 + 1/36 + 1/36 + 1/36 = 4/36 5. (15 pts) A plant is heterozygous only for gene A and gene B, which control different morphological traits (A1A2 B1B2). The alleles of gene A and gene B are incompletely dominant. If the A1A2 B1B2 plant is selfed, how many different phenotypic classes of plants are present in the progeny? A1A1 A1A2 A2A2 assort independently with B1B1 B1B2 B2B2 Heterozygotes have a different phenotype from either homozygote. 9 phenotypic classes corresponding to 9 genotypic classes. A1A1 B1B1, A1A1 B1B2, A1A1 B2B2, A1A2 B1B1, A1A2 B1B2, A1A2 B2B2, etc.4 6. (5 pts) A cactus is heterozygous for completely dominant and recessive alleles of three different genes: Aa Bb Cc The A allele causes long spines, and the a allele short spines. The B allele causes dark green color, and the b allele light green color. The C allele causes yellow flowers, and the c allele white flowers. If the cactus plant is selfed, what fraction of the progeny plants will have short spines, be light green, and have yellow flowers? aa bb C_ 1/4 X 1/4 X 3/4 = 3/64 7. In a hypothetical diploid insect, a triangular body shape is due to a threshold effect: at least than 60 units of “triangle factor” per cell will produce a triangular body shape, and less than 60 units will produce a square body phenotype. Allele triangle+ is a wild-type allele that encodes the triangle factor. Each triangle+ allele contributes 50 units of triangle factor; thus triangle+/ triangle+ homozygotes have 100 units and are phenotypically triangular. A mutant allele triangle- arises; it contributes no triangle factor at all. A. (2 pts) What is the phenotype of triangle- / triangle- homozygotes? square B. (3 pts) What is the phenotype of triangle+ / triangle- heterozygotes? square C. (10 pts) Describe the dominance relationship between the triangle+ and triangle- alleles. (circle one of the four statements below) • triangle+ is dominant to triangle- • triangle- is dominant to triangle+ • triangle+ and triangle- are codominant • triangle+ and triangle- are incompletely dominant5 8. Consider the following pedigree diagram for a rare disease caused by a dominant allele of a single gene (D). (We had not discussed penetrance by class 3, so assume that the allele is 100% penetrant.) A. (2 pts) What is the genotype of the person indicated by the arrow? Dd B. (2 pts) Circle the symbol for the person in the diagram who introduced D into this family. C. (2 pts) Suppose the person indicated by the arrow has children with someone to whom she is not related. What is the chance that her first child will have the disease? The cross is Dd X dd : 1/2 D. (2 pts) What is the chance that her second child will have the disease? 1/2 E. (2 pts) If she has two children, what is the chance that neither of them has the disease? Chance that neither has the disease (both are dd) is 1/2 X 1/2 =