Question

Which vector can clone only a small fragment of DNA?
A. Yeast artificial chromosome
B. Plasmid
C. Cosmid
D. Bacterial artificial chromosome

Answer 1

Hint: Vectors are a transmission agent, which is self -replicating DNA molecules and is used for indirect gene/piece of DNA transfer from one host to another.

Complete answer:
A cloning vector may be a small piece of DNA into which a far off DNA is inserted for cloning purposes. A vector may be a DNA molecule that won’t carry a far off DNA into the host cell. It has the ability to self-replicate and integrate into the host cells.
These vectors play an important role in analysing the molecular structure of DNA. Vectors are often a plasmid from a bacterium, a cell from the upper organism or DNA from an epidemic. The target DNA is added into the vector and is ligated with the help of DNA ligase. The vector transformed into the host cell for the process of replacement.

There are different types of cloning vector:
-Plasmid: A plasmid is a small, extra chromosomal DNA molecule within a cell that can replicate independently of the chromosomal DNA. Plasmid is very small, circular, double stranded DNA molecules found in the bacterium.
Due to the smaller size of plasmid it can clone small fragments of DNA. Expression plasmid are extracted to carry expression signals to ensure maximum expression of the foreign gene. They possess antibiotic-resistant genes along with the high copy numbers. They encode proteins which are necessary for their own replication.
Pbr322, pUC 18, F –plasmid are some of the examples of plasmid vectors.
-Bacterial Artificial chromosomes: It is obtained from naturally occurring F plasmid and it can accommodate large DNA sequences without any risk. These are used to study genetic disorders.
-Cosmid: These are hybrid vectors or recombinant plasmid having a DNA sequence of lambda phage and plasmid DNA. It allows the cloning of large DNA segments upto 50 Kb.
-Yeast Artificial Chromosome: It is used to clone large assemblies of all the genomes of organisms. The average amount of DNA which can be cloned varies from 200-500 Kb.

Hence, the correct answer is option (B).

Note: A cloning vector consists of an origin of replication, restriction sites, antibiotic resistance genes and a reporter gene, whereas an expression vector consists of enhancers, promoters, termination sequences, and transcription and translation initiation sites.