Genetics, Exam 2, Sample A Name ___________________________ 1. A geneticist has one strain of a diploid plant in which the gene orders are AB-centromere-CDEF and KL-centromere-MNO respectively on two of the nonhomologous chromosomes. In another strain of the same plant that arose as a result of X-ray treatment, the gene orders on these two chromosomes are ab-centromere-cno and kl-centromere-mdef. When these two strains are crossed, heterozygous progeny with chromosomes of each type result. a) Show (with diagrams depicting the gene symbols on the chromosomes) how the homologous regions of the chromosomes would pair during Meiosis I Pachytene in these progeny. b) Would all of the gametes resulting from Meiosis in the heterozygous progeny be equally viable? Explain briefly. c) What is this type of chromosomal aberration called? 2. Explain what each of the following terms means: Polyploid Monosomic Trisomic Aneuploid 3. A cross between two strains of Sordaria is analyzed. The relative frequencies of MI/MII asci for each of the two linked genes studied is shown below. What does this information tell you about the order of these genes relative to each other and their centromere? Aa Bb Frequency MI MI High MI MII Low MII MI Medium MII MII Medium 4. A human female with a family history of genetic disorders decides to subject herself to karyotypic analysis and other forms of genetic screening before starting a family. Although none of the known disease genes are found, a rearrangement of genes on one member of a pair of homologous chromosomes is discovered. This rearrangement is diagrammed below. A B C D E F G H I J K L a b c g f e d h i j k l m M a.) What is this type of chromosomal aberration called? b.) Show (with diagrams depicting the gene symbols on the chromosomes) how these homologous chromosomes in this woman would align during Prophase of Meiosis I. c.) What would the consequence of this rearrangement be for this woman and her potential children? 5. A fungus with genotype MP is crossed to a fungus that is mp. The following asci result. Segregation? Ascus Number Type Mm Pp MP MP mp mp 380 MP Mp mP mp 260 MP mP Mp mp 160 MP mp MP mp 60 Mp Mp mP mP 60 Mp mP Mp mP 80 TOTAL 1000 Classify each ascus above as PD, TT, NPD, and MI or MII for each gene. Indicate whether the genes are linked. Determine the map units between each gene and its centromere and between genes. Be sure to indicate the relative order of genes and centromere. 6. The following is the sequence for the template strand of a DNA molecule: DNA Sequence: 5’ C T T T T T T G C C A T 3 ’ a) What is the sequence for the mRNA that would be transcribed from this template? Be sure to indicate 5’ and 3’ ends. b) Using the genetic code table in your text, determine the amino acid sequence that would be translated from this mRNA. 7. In each of the following categories, choose the term that best describes the Watson-Crick (B) structure for DNA? Briefly explain what is meant by each of the terms. A. _______ 1. 2. 3. 4. Parallel Antiparallel Looped Perpendicular B. _______ 1. 2. 3. 4. 5. Double ellipse Left-handed double helix Right-handed double helix Right-handed beta sheet Counter clockwise single helix C. _______ 1. 2. 3. 4. Sugar-base backbone Phosphate –backbone Hydrophobic backbone Sugar-Phosphate backbone 8. In the following diagram showing a replication fork during DNA synthesis, label the appropriate strands as: template, leading, lagging. Circle the location of four of the RNA primers 5’ 3’ 3’ 5’ 9. Fill in each of the blanks with the most appropriate word. Write clearly! Avery, MacCleod and McCarty performed an experiment using Pneumonococcus bacterium that provided strong evidence that the genetic material was DNA rather than RNA or protein. Their experiment was an extension of Griffith’s attempt to develop a vaccine for this bacterium that would protect people against the disease __________________________ When trying to create his vaccine, Griffith killed bacteria by _____________________________ and then injected them into mice. When Avery, MacCleod and McCarty treated partially purified DNA from disease-causing bacteria with ______________________________ then mixed the treated material with non-virulent bacteria and injected it into mice, the mice lived. This provided strong evidence that ____________________ was the genetic material. In the Hershey & Chase experiment, T2 bacteriophage were grown in the presence of radioactive phosphorous (32P) in order to label _______________________ specifically, and radioactive sulfur (35S) was used to label _______________________ specifically. The bacterial cells were separated from virus particles (phage ghosts) using the technique of _________________________. When ____________________________ was used, most of the radioactivity was found in the pellet along with the bacterial cells. 10. In whales, the gene controlling tail shape exists as a dominant notched (T) or a recessive smooth (t) allelic form. A separate gene controls whether there are white markings on the dorsal fin or not. The dominant allele of the second gene (W) results in no white markings whereas the other allele (w) results in white markings in individuals homozygous for the recessive allele. The Tt and Ww genes are linked together and separated by 16 map units. A purebreeding female with a notched tail and white markings on her dorsal fin mates with a purebreeding male with a smooth tail and no white markings on his dorsal fin. One of the F1 females resulting from this cross mates with a homozygous recessive male. What proportion (%) of her progeny would express each of the following phenotypes? Notched tail, white markings on dorsal fin _____________ Notched tail, no white markings on dorsal fin _____________ Smooth tail, white markings on dorsal fin _____________ Smooth tail, no white markings on dorsal fin _____________ 11. In 2010, a new life form is discovered on Pluto. These reptilian-like organisms can have long or short tails, fat or thin legs, and red or yellow skin. A pure-breeding male who has a long tail (t-), thin legs (l+) and yellow skin (y+) is mated with a pure-breeding female who has a short tail(t+), fat legs (l) and red skin (y-). A total of 100 F1 progeny result. All of the F1 progeny have short tails, fat legs and yellow skin (t+l-y+). When the F1 females are crossed to pure breeding males with long tails, thin legs and red skin (t-l+y-), the following phenotypic categories occur in the frequencies shown below. Phenotype Number t+ l+ y+ 2 t+ l+ y20 t+ l- y405 t+ l- y+ 45 t- l+ y+ 450 t- l+ y50 t- l- y3 t- l- y+ 25 Which traits are dominant? Are all of the genes controlling these traits on a single chromosome? If so, what is the order of genes and how many map units lie between each gene pair? 12. The genes A B and C are arranged in that order on a chromosome in Drosophila melanogaster. There are 5 map units between A and B and 10 map units between B and C. What proportion (%) of the progeny from a cross between a AaBbCc female (with all recessive alleles arranged in cis on the same chromosome) and a aabbcc male would you expect to be AabbCc? 13. The original arrangement of genes on fungal chromosomes is shown on the left below. An ascus resulting when this diploid cell underwent meiosis to give rise to haploid spores is shown on the right. Show where any crossovers occurred to give rise to this ascus. 14. If the DNA for a species contains 20% guanine, what percentage of adenine would it contain? 15. If one strand of DNA is made up of 50% purines, what percentage of the complementary strand would be made up of pyrimidines? 16. Draw the strand of DNA that is complementary to the one shown. Be sure to designate which is the 5’ and 3’ end. 5’ A G T C G C T C A G 3’ 17. The N and Z loci are so tightly linked that no recombination is ever observed between them. If NNzz is crossed to nnZZ, and the F1 is intercrossed, what phenotypes will be seen in the F2 and in what proportions? Note: Capital letters are completely dominant. 18. The genes a, b and c are linked with the distance between a and b 15 map units and the distance between b and c 20 map units. In a test cross, what percentage of the progeny phenotypes would you expect to result from double crossovers? ________________________ 19. Indicate whether histone or non-histone proteins are MAINLY responsible for each level of coiling that enables DNA to fit into the compact metaphase chromosome. Histones OR NonHistones Wrapping of DNA around proteins to form a nucleosome involves: Condensation of nucleosome chain into a solenoid structure involves: Looping of solenoid “chord” into a metaphase chromosome involves: 20. List two major chemical differences between DNA and RNA. 21. When Avery and his colleagues had obtained what was concluded to be purified DNA from the IIIS virulent cells, they treated fractions of the extract with protease, RNase, or DNase then evaluated each treated extract to determine if it had lost or retained its ability to transform non-virulent bacteria into virulent SIII bacteria. What happened when the DNA extract was treated with protease and why?