Question

Which of the following is required for an insertion sequence element in E. coli to be able to transpose?

		A gene for reverse transcriptase and long terminal repeats
		A gene for reverse transcriptase and inverted repeats
		A gene for transposase and inverted repeats
		A gene for transposase and long terminal repeats
		A gene for DNA polymerase and long terminal repeats

Which type of deletions and/or insertion would not lead to frameshift mutations?

		A deletion that removes only a single amino acid
		A deletion that removes a multiple of three amino acids
		An insertion that comes after the start codon
		A deletion that comes after the start codon
		Any type of deletion or insertion will lead to a frameshift mutation.

All of the following are requirements of a bacterial cloning vector EXCEPT:

		Origin of replication
		Unique restriction enzyme sites
		Ti plasmid
		Selectable

Using Table 1 above again, determine the approximate frequency of the Lw allele in the population:

		0.357
		0.468
		0.490
		0.561

Answer 1

Correct answers-

1. A gene for transposase and inverted repeats is required for an insertion sequence element in E. coli to be able to transpose.

Transposon also called as jumping gene or transposable element is mobile genetic elements i,e these are the sequence present in the DNA which can change their position within the genome of an orgnism, they may lead to ceretain types of mutations like deletion or duplication

Generally two classses of transposones are present

1. Class I or retrotransposons present in many higher organisms. they work by copy and paste mechanism using reverse transcriptase enzyme. Also instead of inverted repeats long terminal repeats are generally present in retrotransposons.

2. Class II or DNA transposons present mainly in lower organisms like prokaryotes. they work by cut and paste mechanism by encoding an enzyme transposase.  transposase cleave the ends of the transposon which has to be move and also target sites where the element has to be inserted. these Class II transposons are flanked by terminal inverted repeats at both ends. these repeats defines the boundaries in transposons so that it can be recognized by transposase and thus helps in transposition.

So, all other options except for option 3 (A gene for transposase and inverted repeats) are wrong.

2. A deletion that removes a multiple of three amino acids would not lead to frameshift mutations.

Frameshift mutation happenes due to deletion or insertion of one or more new nucleotides in the DNA sequence so that from the point of insertion or deletion DNA sequence will be read out of frame. Because gene expression is based on triplet nature of codons, these deletion or insertion leads to change in the reading frame, so that the polypeptides coded by new codons are completely different from the original one.

Since codons are triplet in nature so if a deletion removes a multiple of three amino acids then this would not lead to frameshift mutations but may leads to production of shorter polypeptide chain then normal.

3. Ti plasmid is not among one of the requirements of a bacterial cloning vector.

A clonig vector is used for cloning purposes in which a small fragment of DNA in which foreign DNA fragment can be inserted then it is transformed in an organism where it can replicate and make multiple copies. thus cloning vectors are used for cloning purposes.

Origin of replication required for replication of the vector within the host, so that it can make multiple copies.

Unique restriction enzyme sites are required so that foreign DNA fragments could be inserted and replicated along with vector.

Selectable markers are required so that we can saperate non transformed host cells with transformed host cells. and only cells containing our gene of interest or vector can be able to grow in certain media.

Ti plasmid- it helps in transformation as well as integration of a gene or DNA segment into the genome of the host. and if we need to clone something we do not want to integrate it into the genome of the host.

So, All of the following are requirements of a bacterial cloning vector EXCEPT 'Ti plasmid'.

4. Table is not provided.