Question

Give an account of artificial chromosomes in the transfer of genetic material.

Answer 1

Artificial chromosomes used for the transfer of genetic materials are :

(i) YAC Vectors. Yeast artificial chromosomes (YAC) have been developed as a high capacity vector which can clone a very large DNA segment of about 1 Mb in length. It is maintained as a separate chromosome in the cell. It has been used for the physical mapping of human chromosomes in the ‘Human Genome Project’. The YAC plasmid contains the E. coli origin of replication (ori^E) and a selectable marker (amp^r), a yeast DNA sequence, genes each for uracil biosynthesis pathway (URA3) providing centromeric function (CEN), automatic replication sequence (ARS), tryptophan synthesis pathway (TRP) and telomeric (T) sequence (Fig.). There are recognition sites for restriction enzymes such as Smal and BamHI.

A yeast artificial chromosome (YAC) vector

(a) BAC Vectors: Bacterial artificial chromosomes (BAC) are used as cloning vectors. BAC is constructed by using Fertility of F factors (present on F plasmid) of E. coli. BAC vectors contain ori gene, a gene for maintenance of F factor, a selectable marker (an antibiotic resistance gene) and many restriction sites for insertion of foreign DNA. The upper limit of foreign DNA to be inserted in BAC is about 300-3500 kb. It is used in geneome sequencing projects.