DNA Replication & Structure Exam

Examination Instructions

• Put your name on each page.
• Read each question carefully.
• Place all answers in the space provided, using a pen.
• You have 75 minutes for the exam.

Multiple Choice Questions

• Heat disrupts hydrogen bonding in DNA strands.
• DNA strands with higher GC content require higher temperatures to denature.
• A DNA molecule with 50 base pairs containing 15 cytosine bases has 35 thymine bases, because A pairs with T, and G pairs with C, so A+T must equal 50x2 - 15x2 = 70, so A+T=35.
• A sequence that can form a hairpin is 5'-GGGGTTTTCCCC-3', because the sequence can fold back on itself and form a stem-loop structure.
• A-form DNA is most likely to be seen in an ancient dehydrated tissue sample
• DNA polymerases cannot synthesize DNA from scratch without a primer.
• In a replication bubble diagram, strand 'B' represents a lagging strand.
• Ligase does NOT aid in the unwinding of DNA during replication.
• Telomerase uses an RNA template to synthesize new DNA.
• Prokaryotic promoters contain the sequence TATAAT at a position -10 from the transcription start.
• Multifactorial traits are influenced by multiple genes and the environment.
• The diagram represents RNA transcripts of different lengths depending on where the transcription begins on the DNA template.
• The RNA sequence transcribed from the given DNA sequence is 5'-GGCAUAUUACA-3'.
• Polydactylous persons with extra fingers or toes can have variable expressivity.
• The regression coefficient measures the slope of the line depicting the relationship between two variables.
• The relatively small amount of genetic differences between some species suggests that many phenotypic differences reflect changes in gene expression rather than the evolution of new genes.
• Cock feathering in domestic chickens, an autosomal recessive trait expressed in males only, is an example of sex-influenced inheritance.
• Cytoplasmically inherited traits are usually inherited from one parent, typically the maternal parent
• Human eye color exemplifies polygenic inheritance, meaning multiple genes contribute to the trait.
• A single mRNA transcript generated from multiple separate pre-mRNAs is an example of transplicing.
• Telomeres of some birds getting longer with age is false, rather, they get shorter.
• A type of repetitive DNA found in tandem repeats in centromeres is satellite repeats.
• Quantitative characters often exhibit a normal distribution
• DNA found in Greenland’s permafrost could have derived from all of the above, i.e., skin, feces, urine, and hair or feathers
• A Gene X highly expressed in brain tissues but not in the heart suggests that a transcriptional activator that binds to the regulatory promoter of Gene X is present in brain tissue but not in heart tissue.
• DNA fingerprinting for forensics involves measuring the number of repeated segments in microsatellites.
• Seeing a gene that encodes a reverse transcriptase in genomic DNA suggests that region contains a LINE or ERV.
• Gene expression patterns related to enhancer and promoter regions suggest that Gene 2 will be expressed in both brain and salivary gland cells.
• To determine if mutations in two dogs with the same phenotype are in the same or different genes, a complementation test is performed.
• Plasticity is the capability of a single genotype to produce a range of potential phenotypes because of environmental effects.
• Scale color in fish where two green fish produce offspring with a 12/16 green, 3/16 yellow, and 1/16 white ratio, the gene interaction is most likely to be dominant epistasis.

Fill In the Gaps

• Mutations in hox genes cause parts to appear in the wrong segments; these are called homeotic mutations.
• ERV stands for endogenous retrovirus.
• Histone proteins (2a, 2b, 3, 4) form a nucleosome to compact DNA.
• A nested gene sits in the intron of another gene
• Primase produces a short stretch of RNA primer during DNA replication

Genome Composition

• Genome is composed of:
• Exons
• Introns
• Regulatory sequences
• Repetitive DNA

True/False Statements

• Some DNA polymerases can function in DNA repair mechanisms - TRUE
• Dominant alleles on one chromosome and recessive alleles on the other describe the cis configuration - TRUE
• Heterochromatin unpacking during interphase while euchromatin stays folded - FALSE
• Acetylation of lysine's on histone tails tightens packing of DNA around nucleosomes and decreases expression - FALSE
• The extension at the 3' overhang by telomerase is followed by the extension of 5' complementary strand via a currently unknown mechanism - TRUE
• DSCAM can produce more than 38,000 different mRNAs because it has that many 3' cleavage sites - FALSE
• The Drosophila Fruitless gene is called a behavioral switch gene because its action is necessary and sufficient to produce a particular behavior - TRUE

Diagrams

• Diagrams of DNA molecules need to be labeled for 5' and 3' ends, hydrogen bond, phosphodiester bond, a purine, a pyrimidine, and a deoxyribose sugar.

Cystic Fibrosis Bonus Points

• Alternative splicing of CFTR pre-mRNAs in cystic fibrosis patients can be supported if CFTR mRNAs that exclude Exon 16 are more common in individuals with the mutation, while CFTR mRNAs that include Exon 16 are more common in individuals without the mutation.