Question

1. A plasmid is a

A. Small circular segment of the endoplasmic reticulum that binds the lacI repressor gene product.

B. Segment of the bacterial genome that has been digested with a restriction endonuclease.

C. Small circular segment of DNA that lacks an origin of replication (Ori)

D. Small, circular segment of DNA that frequently contains antibiotic resistance genes.

E. Segment of the nucleosome that has been digested with a restriction endonuclease.

2. Evidence that the lacI repressor gene works in trans is provided by the observation that:

A. Expression of the wild type repressor from a plasmid will confer inducible behavior on a chromosomal lac operon when the chromosome encodes a non-functional repressor.

B. Expression of the wild type repressor from a plasmid will confer constitutive behavior on a chromosomal lac operon when the chromosome encodes a non-functional repressor.

C. Expression of the wild type repressor from a plasmid will block expression of a chromosomal copy of the lac operon in the absence of glucose.

D. Expression of a non-DNA binding repressor from a plasmid will confer constitutive behavior on a chromosomal lac operon when the chromosome encodes a functional repressor.

E. Expression of the cAMP-CAP complex blocks interaction of repressor with the operator.

3. A “leaky” promoter means:

A. Mutations have decreased the affinity of the promoter for RNA polymerase.

B. Transcription is induced by lactose.

C. A gene is expressed in response to a repressive signal

D. A low level of transcription occurs in the absence of a transcription-inducing signal.

E. RNA polymerase switches from an active to an inactive form.

4. One result of histone acetylation can be

A. Removal of all nucleosomes from a specific gene.

B. Addition of nucleosomes causing tighter chromatin packing.

C. Increased mobility of nucleosomes and DNA in chromatin.

D. Degradation of DNA within the nucleosome.

E. Protease degradation of the TATA binding factor.

5. Prior to trait mapping, it is best to:

A. Develop lines that are incapable of recombination.

B. Isolate the smallest possible population of test subjects.

C. Insure that there are limited numbers of SNPs in the population you are studying.

D. Identify pure breeding lines for the trait to be studied.

E. Sterilize all animals carrying trait to be studied.

Answer 1

1. answer D. Small, circular segment of DNA that frequently contains antibiotic resistance genes.

Plasmid is a double stranded, circular extrachromosomal DNA found in certain bacterial cells, which can replicate independently and often carry antibiotic resistance genes

2. A. Expression of the wild type repressor from a plasmid will confer inducible behavior on a chromosomal lac operon when the chromosome encodes a non-functional repressor.

Lac repressor protein is encoded by lac I gene which will go and bind to the operator DNA region of the lac operon and stop the RNA polymerase from binding to the promoter and initiating the transcription. Trans regulatory factor is a protein from a different gene which regulates the expression of a gene away from its gene sequence.

3. D. A low level of transcription occurs in the absence of a transcription-inducing signal.

A leaky promoter will drive the mRNA production at low level even when it is not been induced.

4.C. Increased mobility of nucleosomes and DNA in chromatin.

Acetylation weakens the histone -DNA contact there by increasing the nucleosome mobility in the DNA