Bio 309 Exam 1 Study Guide
Bio 309 Exam 1 Study Guide BIOL 309
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This 4 page Study Guide was uploaded by Amanda Tobias on Monday February 29, 2016. The Study Guide belongs to BIOL 309 at Towson University taught by Dr. Masters in Spring 2016. Since its upload, it has received 244 views. For similar materials see Genetics in Biology at Towson University.
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Date Created: 02/29/16
You should review all previous quizzes and all previous study guides. Suppose you were looking at a simple, Mendelian trait. For seed shape in peas, round (R) is dominant to wrinkled (w). If you crossed a round pea plant with another round pea plant, what would the genotypes of your parental plants be if all offspring had round peas? o RR and rr What if some offspring had wrinkled peas? o Rr and rr What fraction of the offspring should have wrinkled peas if any of the offspring have wrinkled peas? o 1/4 If you cross two plants with smooth peas, what will be the phenotype(s) of the offspring? o Depends if the parents are heteroxygous or homozygous True or false: Most traits are controlled by a single gene, like height in Mendel’s peas. o False What percentage of genes on the Xchromosome has been connected to normal intelligence in humans? o 10% Why was the Xchromosome used in the experiments we discussed? o Because in males there is only one x chromosome o The experiments were done on males so if there was a change in genotype on the x chromosome you would be able to How many genes in total would you guess in the human genome are likely to be connected to normal intelligence? o 3200 How many genes are on a typical human chromosome? o 2025,000 Is it surprising that trisomy 21 is the least severe of the trisomies? Please explain your answer. o This is not surprising. Chromosome 21 is very small compared to the lower number chromosomes so it makes sense that it is least severe. Trisomy of other chromosomes are so severe that you never see it because the person dies before they are born. th Experiments on flies in the early part of the 20 century demonstrated that the genetic material was carried on chromosomes. Did this demonstrate that DNA must be the genetic material? Explain why, or why not. o This did not demonstrate that DNA was the genetic material. o Thomas Morgan did experiments with eye color that was sexlinked in drosophila. He found that whenever there was a strange phenotype, there was also something strange with the chromosomes. Which experiments more conclusively showed that DNA was the genetic material, those by Avery, McCarty and MacLeod, or those by Hershey and Chase? Please explain why. o Those by Avery, McCarthy and MacLeod showed that DNA was the genetic material more conclusively than those by Hershey and Chase. o In Hershey and Chase experiement, there was still some protein found in the pellet even though it was mostly DNA o When Avery, McCarty and MacLeod treated the transforming material with protease it still worked,but when they treated it with DNase it no longer worked. Which of the following would necessarily prove that protein is NOT the genetic material in the Hershey and Chase experiments? a. When phage is labeled with radioactive phosphorus, NO radioactivity is observed in the supernatant. b. When phage is labeled with radioactive sulfur, NO radioactivity is observed in the supernatant. c. When phage is labeled with radioactive sulfur, NO radioactivity is observed in the cell pellet. d. When phage is labeled with radioactive phosphorus, NO radioactivity is observed in the cell pellet. What are Barr bodies? o Barr bodies are the condensed X chromosomes If you were to see the equivalent of Barr bodies in insects, in which gender would they be found? o Female Why don’t insects have Barr bodies? o Instead of inactivating one x chromosome in females, the single x chromosome in males is hyperactivated If you were to see the equivalent of Barr bodies in birds, in which gender would they be found? o Males Why are Y and W chromosomes so small? o The Y and W chromosome have no ability for recombination. o Therefore, if there is a mutation on that chromosome there is no way to get rid of that mutation o It will just continue to be passed down to the offspring that receive a y or w chromosome o Over time, evolution has caused the chromosome to become very small in order to prevent mutation from occurring Are mutations scrubbed more slowly from X chromosomes than autosomal chromosomes in placental mammals? o They are scrubbed away more slowly from X chromosomes In drosophila, chromosomes do not undergo recombination in males. Would you expect mutations to be scrubbed more slowly from X chromosomes than autosomal chromosomes in drosophila? o Yes Why are males a major cost of sex? o Females produce both male and female offspring o The male offspring are not capable of producing offspring on their own You are studying a genetic disease in children and you discover that it is more common in children that have older fathers. (The condition is much more common in children with fathers over the age of 40 than children with fathers under the age of 30.) Maternal age doesn’t seem to be important. You suspect what type of mutation? o Point Mutations o De Novo mutation What are GWAS analyses, and what are they used for? o GWAS analyses take the genomes of different people with and without specific diseases and see if there are SNPs on specific chromosomes that are more strongly associated with the disease Look at slide 3 from 21016. What do the series of dots above the number 19 indicate? o The dots indicate specific SNPs on chromosome 19 that are found more often in people with high risk for microcirculation Why are the dots all stacked on top of each other? o They are different SNPs so they have different significance of actually being related to microcirculation Are there any alleles on chromosome 3 that are associated with increased risk for microcirculation? o No The two strands of a DNA molecule are held together by what types of bonds? o Hydrogen What effect does having lots of C’s and G’s have on how tightly the two strands stick to each other? o The more c’s and g’s there are the tighter the strands stick together. The C and G pair stacks better than the A T pair and has more hydrogen bonds Why do C’s and G’s have this effect? o They have this effect because they stack more tightly and have 3 hydrogen bonds instead of two Would you expect origins of replication to be GCrich or ATrich? Why? o AT rich o AT bonds are weaker so it would be easier to separate the two strands there If you could only choose one of DNA, RNA or proteins, which would you pick to make a functional, self replicating entity? Please explain your answer. o DNA because it is the only one that is double stranded and able to self replicate If uracil were normally found in DNA, would you expect the mutation rate to be higher? Please explain your answer. o Yes o The uracil glycosylase is able to recognize uracil because it isn’t a normal DNA base o If it were a normal base in DNA, it would be difficult to tell which base was correct and DNA polymerase would have to guess Why does 5’3’ synthesis make repair easier? o 5’3’ synthesis brings energy with the nucleotide it is adding o If it were opposite, there would have to be another step to recharge nucleotides after one was removed in order to fix the problem and add another one. Why does the ratio of 5’3’ polymerase activity to 3’5’ exonuclease activity affect the mutation rate? o If the 5’3’ polymerase activity were too much the DNA would be replicating too quickly and would make more mistakes o If the polymerase activity were decreased then it would be slower and probably make less mistakes. o The 3’ to 5’ exonuclease activity is the proofreading function and if it is increased it slows down the polymerase activity and creates less mutations. But if it is decreased it speeds up the polymerase activity and creates more mutations. o This ratio is important to keep the amount of mutations small If the ratio increases (i.e., 5’3’ polymerase activity increases relative to 3’5’ exonuclease activity), what happens to the mutation rate? o Increases Explain how base tautomerization can lead to mutations. o Tautomerization is when a base spontaneously switches into its rare form o This can lead to mutations if the rare form is replicated instead of the base that is supposed to be there o This results in a mismatch How does the 3’5’ exonuclease help? o The exonuclease can recognize an incorrect base pair that occurs while replicating and chew back to replace it with the correct base pair. o If that happens Would tautomerization cause mutations if there was no DNA replication? o No because the bases switch between forms fluidly so if it wasn’t being replicated, there wouldn’t be the chance of the incorrect form being replicated What is the error rate of DNA polymerases? What is the error rate of RNA polymerases? 5 6 o The error rate for DNA polymerase is 14 to 10 o The error rate for RNA polymerase is 10 What accounts for the difference? o The difference is caused by the 3’ to 5’ exonuclease activity proofreading function Which of the following is true regarding the deamination of cytosine and the deamination of 5methy cytosine? a) a deaminated 5methyl cytosine is repaired by mismatch repair b) a deaminated 5methyl cytosine is more likely to result in a mutation than a deaminated cytosine c) repair of deaminated cytosine will require uracilDNA glycosylase d) all of the above e) none of the above When guanine deaminates, it forms xanthine. Xanthine pairs with thymine. Suppose DNA normally had xanthine instead of adenine. Which of the following would you expect to be true? a) guanine deamination would be repaired by mismatch repair b) guanine deamination would be a significant source of mutation c) repair of guanine deamination would be the same as it currently is in our cells d) all of the above e) a and b, but not c How does methylation of DNA make mismatch repair more accurate? o When there is a methylated C on one strand of DNA, there is always a methylated C on the complementary strand of DNA also. o For a short time after DNA is replicated, the new strand is not yet methylated o If mismatch repair finds the mutation before the new strand is methylated, it can tell the new strand apart from the old strand. This allows it to assume that the base on the old strand is correct and it doesn’t have to guess which base of the mismatch to chagne What do all known DNA polymerases require? o A DNA or RNA primer What enzymes are necessary for leading strand synthesis? What about lagging strand synthesis? o In both leading and lagging strand synthesis, DNA polymerase, helicase, topoisomerase, telomerase, and single stranded binding proteins are needed o In lagging strand synthesis, ligase is also needed What would an inhibitor of ligase do to DNA synthesis? Would it affect leading strand synthesis? Would it affect repair? Would it affect mutation rates? Explain why, or why not. o An inhibitor or ligase would make it impossible to replicate the lagging strand of DNA o It would create fragments with broken sugar phosphate backbone that are not sealed together and therefore can’t be copied Explain why telomerase is needed to replicate the ends of DNA molecules. Which strand is it needed for? o Telomerase is needed to replicate the 3’ end of the DNA strand because there isn’t a DNA polymerase coming from the end to remove the RNA primer. Without telomerase, every time DNA was replicate you would lose a segment form the end Suppose you had a drug that activated telomerase in somatic cells. What effect would you expect it to have on longevity? How about cancer rates? Please explain your answers. o It would increase lifespan because it would slow down the aging process o It would also increase cancer rates because the cells would be able to replicate as they aged and developed defects. Those defects could cause cancer and if they are able to replicate the cancer would be more likely What is the size of the human genome? o 3 billion base pairs What is the size of the human exome? (What is an exome? Does it include exons, 3’UTRs, introns, the regions upstream of the start of transcription that control transcription rates?) o 40 million base pairs o The exome includes exons and 3’ and 5’ utrs How does the size of the human genome and exome compare with that of other complex organisms (salamanders, birds, insects, trees, etc.)? o The human genome is much larger than that of other complex organisms o The human exome is about the same size as that of other complex organisms What are the effects of UV radiation on DNA? How is that repaired? o UV radiation causes mutations such as thymine dimers and bulky lesions in DNA o To repair this, UVR proteins cut out the chunk of nucleotides around the thymine dimer or bulky lesion. DNA polymerase then comes in and puts the correct nucleotides back in and ligase seals the gaps What are the effects of xrays on DNA? Explain how this might be similar to reduced ligase activity. What are the effects of microwaves on DNA? o Xrays can break the sugar phosphate backbone and cause deletions, duplications, inversions, and translocation. o This is similar to reduced ligase activity because without ligase the sugar phosphate backbone would have breaks in it already o Microwaves don’t affect DNA
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