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Artificial Chromosomes as Vectors

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Estimated time: 12 minutes
CISCE: Class 12

Introduction

Artificial chromosomes are specially constructed DNA segments used to transfer genetic material into eukaryotic cells. They are made from bacterial or yeast components and are called Bacterial Artificial Chromosomes (BACs) and Yeast Artificial Chromosomes (YACs).

CISCE: Class 12

Bacterial Artificial Chromosomes (BACs)

  • Derived from the F (fertility) plasmid of bacteria.
  • Used for cloning large DNA segments of about 100–300 kb, and can accept inserts up to 300–350 kb.
  • Host organism: E. coli*.
  • More stable than YACs.
  • Maintain low copy number, controlled by the F-plasmid.
  • Important elements: oriS, repE, parA, parB, antibiotic resistance markers, T7 and SP6 phage promoters.
  • Main uses: whole genome mapping and sequencing projects in microbes, plants and animals; used as vectors in the Human Genome Project (HGP).

Bacterial artificial chromosome (BAC)

CISCE: Class 12

Yeast Artificial Chromosomes (YACs)

  • Constructed by joining segments of original yeast (Saccharomyces cerevisiae) DNA with a linear bacterial plasmid.
  • Contain telomeric, centromeric and origin of replication (ori) sequences, forming a small complete yeast chromosome.
  • Specially designed for eukaryotic gene transfer and are more efficient than simple plasmids for this purpose.
  • Can accept very large DNA fragments, up to about 1 million base pairs.
  • Include ori and selectable markers such as ampicillin resistance (amp) gene.
  • Used to clone large DNA pieces and as vectors in the Human Genome Project (HGP).

Yeast artificial chromosomes (YAC)

CISCE: Class 12

Key Points: Artificial Chromosomes as Vectors

Feature Bacterial Artificial Chromosomes (BACs) Yeast Artificial Chromosomes (YACs)
Source Derived from bacterial F-plasmid Derived from yeast (Saccharomyces cerevisiae) DNA
DNA insert size 100–300 kb (up to 350 kb) Up to 1 million base pairs
Stability More stable Less stable than BACs
Host cell E. coli Yeast cells
Important elements oriS, repE, parA, parB, antibiotic resistance, T7 & SP6 promoters Telomere, centromere, ori, selectable markers
Main use Genome mapping and sequencing Cloning very large eukaryotic genes
Special feature Maintains low copy number Behaves like a true yeast chromosome
Application Used in Human Genome Project (HGP) Used in Human Genome Project (HGP)
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