Genetics Final Exam 2023

What modification neutralizes the charges on histones and looses up the interactions between histones and DNA? - Answer- ACETYLATION Two types of post-transcriptional modifications that take place in the mRNA of eukaryotes - Answer- the addition of a CAP at the 5' end of the transcript and the addition of a POLY A sequence at the 3' end of the message Nucleic acid blotting is widely used in recombinant DNA technology. In a Southern blot one generally - Answer- Hybridizes filter-bound DNA with DNA probe Assembly of basal transcription factors begins at the _______ sequence in the promoter. - Answer- TATA or "TATA box" All of the following may result from promoter mutations except: (A) Decreased affinity for RNA polymerase (B) Increased affinity for RNA polymerase (C) Mutant RNA polymerase (D) Unregulated transcription (E) A new phenotype - Answer- (C) Mutant RNA polymerase Imprinting is DNA modification in gametogenesis that effects gene expression in the zygote. - Answer- Occurs in the GERM line, accompanied by HEAVY METHYLATION. Once imprinted on, a SILENCED gene remains inactivated during EMBRYOGENESIS. RNA interference (RNAi) - Answer- Triggers DEGRADATION of RNA transcripts containing homologous sequences Consider a eukaryotic transcriptional activator protein that binds to an enhance sequence and promotes transcription. What change in regulation would you expect from a duplication in which several copies of the enhancer were present instead of just one? - Answer- INCREASED TRANSCRIPTION Which of the following enzymes synthesizes DNA from a single stranded RNA template? (A) Reverse Transcriptase (B) DNA polymerase (C) RNA polymerase (D) Ligase (E) Endonuclease - Answer- (A) REVERSE TRANSCRIPTASE A genetic characteristic often associated with mutations caused by insertion of a transposable element is ________. - Answer- (B) INSTABILITY ****add definition Ultraviolet light primarily damages DNA by - Answer- forming PYRIMIDINE dimers A chromosome in which linear order of a group of genes is the reverse of normal order has an - Answer- INVERSION ***add definition Meiosis - Answer- involves one round of DNA replication and two rounds of cell division Which of the following procedures is used to produce a genetic map of a eukaryotic chromosome? (A) hybridizing fluorescently-tagged genes to whole chromosomes, then observing which chromosomes light up under the microscope (FISH) (B) test-crossing genetic markers to determine their relative distances in cM (C) sequencing the entire genome and predicting gene locations using a computer algorithm (D) staining whole chromosomes with giesma to visualize G-bands under a microscope (E) both A and D - Answer- (B) test-crossing genetic markers to determine their relative distances in cM ****add definition The cross AABB x aabb is made, and the F1 (AaBb) is back-crossed to the double recessive parent (aabb). If these two loci are 10 centimorgans apart (r=0.10) what is the expected frequency of AaBb in the resulting progeny? - Answer- 45% ***WHY??? A mutant microorganism is unable to synthesize an essential compound but able to grow if that compound is supplied exogenously is an - Answer- AUXOTROPH **add definition The F factor qualifies as an episome because it - Answer- can exist either SEPARATE from the chromosome or INCORPORATED into it In a mating between Hfr and F- cells, the F- recipient - Answer- REMAINS F- Identify labeled part (A) of a typical eukaryotic gene and give a brief description of its function. - Answer- (A) ENHANCER: enhancer elements are bound by transcription factors (TF) or transcriptional activators. Enhancers work upstream or downstream of the promoter, in either orientation, and from far away the activation domain of the TF will interact with the basal transcription machinery including RNA polymerase and increase the amount of txn from a promoter. Identify labeled part (B) of a typical eukaryotic gene and give a brief description of its function. - Answer- (B) TATA BOX: A DNA sequence at which RNA polymerase binds and initiates transcription in eukaryotes the highly conserved sequence is the TATA box. Identify labeled part (C) of a typical eukaryotic gene and give a brief description of its function. - Answer- (C) EXONS: the sequences in a gene that are retained in the mRNA even after introns are removed (to code for the final product). Identify labeled part (D) of a typical eukaryotic gene and give a brief description of its function. - Answer- (D) INTRONS: A noncoding DNA sequence/section in a gene that is transcribed but then excised from the primary transcript in forming mature mRNA molecules. Identify labeled part (E) of a typical eukaryotic gene and give a brief description of its function. - Answer- (E) POLYA tail: the poly-A tail is a long chain of adenine nucleotides that is added to a mRNA molecule during RNA processing to increase the stability of the molecules - OR - when RNA polymerase II reaches a "termination sequence" (TTATT on the DNA template and AAUAAA on the primary transcript), the end of transcription is signaled even through I have TTTTTT's. How do a mutation and a SNP differ? - Answer- Formally, a mutation is a change in the DNA without regard to whether or not it is causing a phenotypic change - present at less than 1% in the population. A single nucleotide polymorphism is a sequence variant that is present at a frequency of 1% or higher in a population, regardless of functional consequences. The difference depends on the prevalence in the population. You undertake a genetic screen with chemical mutagen EMS to isolate four different C. elegans mutants that have an abnormal crawling behavior. Using a genetic complementation approach you discover all four mutants are alleles of the same gene. By analyzing the phenotypic results of combinations of the unc alleles you generate the following pairwise matrix. (A) Based on the data make a hypothesis about the genetic nature of the unc-1 and unc-2 alleles, what classification would best describe each unc allele and briefly justify your answer. - Answer- unc-1 is a null or amorphic mutation. It likely has no function and therefore results in a dead phenotype as the worm can't move to eat. unc-2 is a hypermorphic mutation that results in increased gene expression or gene function result in increased locomotion. You undertake a genetic screen with chemical mutagen EMS to isolate four different C. elegans mutants that have an abnormal crawling behavior. Using a genetic complementation approach you discover all four mutants are alleles of the same gene. By analyzing the phenotypic results of combinations of the unc alleles you generate the following pairwise matrix. (A) Based on the data make a hypothesis about the genetic nature of the unc-3 and unc-4 alleles, what classification would best describe each unc allele and briefly justify your answer. - Answer- unc-3 is hypomorphic mutation resulting in a gene product with some function or some level of expression. The resulting phenotype is a slow moving worm. unc-4 is also a null or amorphic mutation You undertake a genetic screen with chemical mutagen EMS to isolate four different C. elegans mutants that have an abnormal crawling behavior. Using a genetic complementation approach you discover all four mutants are alleles of the same gene. By analyzing the phenotypic results of combinations of the unc alleles you generate the following pairwise matrix. (B) Explain how a cross between unc-1 and unc-4 could result in dead worms - Answer- Both alleles are SEPARATE NULL or AMORPHIC MUTATIONS, therefore a cross of unc-1 and unc-4 worms results in a dead phenotype as would a HOMOZYGOUS unc-1 worm. Mutations can be detected by a variety of methods that do not require directly manipulating an organisms DNA sequence; briefly describe two. - Answer- Mutations can be inferred from an organisms biochemical or morphological phenotype e.g. scoring PKU or polydactyly. Large-scale mutations resulting in aneuploidy may be detecting by examining an organisms karyotype, either by CHEF electrophoresis, or directly staining and visualizing stained chromosomes from, for example: cheek, salivary glands or placenta. Mutations can be detected by methods that do directly manipulate an organisms DNA but do not require DNA sequence analysis; briefly describe two. - Answer- Mutations can be detected electrophoretically by doing protein electrophoresis and scoring novel alleles, by restriction fragment analysis of PCR amplified sequences, by performing RAPD analysis, detecting the numbers an