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BIOL 2107 Study Guide - Midterm Guide: Heteroduplex, Spo11, Phosphodiester Bond

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9 Apr 2016

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Carleton University

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Crossing over is an important source of new combinations of alleles. (a) outline the steps involved in crossing over initiated by the dmc1 protein (2 marks). Dmc1 breaks phosphodiester bonds of both strands of one chromatid. Spo11 in yeast is homologous to dmc1 of multicellular eukaryotes. Step 2 in the model of recombination: resection. 5" ends of each broken strand are degraded to create 3" single-stranded tails. Step 3 in the model of recombination: first strand invasion. One single-strand tail invades a non-sister chromatid and forms stable heteroduplex. Displacement loop (d-loop) from invaded chromatid is stabilized by single-strand binding protein. Step 4 in the model of recombination: formation of double holliday junctions. D-loop enlarged by new dna synthesis at 3"-end of invading strand. New dna synthesis fills in gap in bottom strand using displaced strand as template. Step 5 in the model of recombination: branch migration. Heteroduplex region of both dna molecules is lengthened.

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Related Questions

Question 1

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_____________ are physical microscopicevidence of crossing over.

a. Recombinants

e. DNA double strand breaks

Question 2

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In a 3 point cross, the recombinantphenotypes corresponding to ___________ are the leastfrequent.

a. single crossover events

b. F2 recombinants

c. double crossover events

d. parental recombinants

e. F1 recombinants

Question 3

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You perform a tetrad analysis experiment inNeurospora to determine the position of a single gene (z) relativeto the centromere. You obtained the following numbers of tetradsordered from the top of the ascus to the bottom. What is the mapdistance between the z gene and the centromere in map units? 379 z+z+ z+ z+ z z z z 421 z z z z z+ z+ z+ z+ 65 z z z+ z+ z z z+ z+ 35z+ z+ z z z+ z+ z z 54 z+ z+ z z z z z+ z+ 46 z z z+ z+ z+ z+ z z(Note: if the genotypes don't align well in the online assignment,see the PDF that was uploaded as well)

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Injection of mice with Streptococcuspneumoniae that grow as smooth colonies in culture results in_________.

a. none of the other answers

b. chronic pneumonia

c. no phenotype

d. embryonic lethality

e. death of the mice

Question 5

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The transforming principle studied by Avery,MacLeod, and McCarty could be destroyed or removed by_________.

c. ultracentrifugation

e. shear forces.

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The Hershey-Chase Waring blender experimentdetermined that _________________________.

a. bacteriophage replicate by semi-conservativeDNA synthesis.

b. all of the other answers are correct.

c. bacteriophage integrate into the hostgenome, becoming insensitive to external shear forces.

d. radiolabelled bacteriophage DNA enters hostcells during infection but that radiolabelled proteins do not

e. bacteriophage are made up of roughly equalamounts of protein and DNA using radioactive sulphur andphosphorous.

Question 7

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All DNA polymerases synthesyze DNA in a__________.

a. N-terminal to C-terminal direction.

b. 5' to 3' direction.

d. 3' to 5' direction.

e. C-terminal to N-terminal direction.C-terminal to N-terminal direction.

Question 8

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Meselson and Stahl used a _______ isotope of____________ to disprove the conservative and dispersive models ofDNA replication.

a. heavy, sulphur

b. radioactive, nitrogen

c. heavy, nitrogen

d. radioactive, sulphur

e. radioactive, phosphate

Question 9

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DNA replication is initiated at________________ of replication.

a. semi-conservative sites

d. bidirectional sites

e. termination sites

Question 10

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In bacteria, initiation of DNA replicationrequires ____________________.

a. primase to synthesize a short DNAprimer.

b. nuclear DNA binding proteins.

c. a replication fork.

d. a terminal 3'OH group on DNA.

e. primase to synthesize a short RNAprimer.

Question 11

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DMC1 protein facilitates strand invasionduring _______.

a. double strand break repair.

b. resolution of holliday junctions.

c. branch migration.

d. meiotic recombination.

e. mitotic recombination.

Question 12

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Resolution of holliday junctions in the sameplane results in _______.

a. genetic loss.

b. meiotic crossover.

c. failed crossover.

d. homoduplex formation.

e. bidirectional fork migration.