Minichromosome

Overview
A minichromosome is a small chromatin-like structure consisting of centromeres, telomeres and replication origins and little additional genetic material. They replicate autonomously in the cell during cellular division. The origin of minichromosomes is the result of natural processes (chromosomal aberrations) or genetic engineering.

Structure
Minichromosomes can be either linear of circular pieces of DNA. By minimizing the amount of unnecessary genetic information on the chromosome and including the basic components necessary for replication (centromere, telomeres, replication sequence), scientists aim to construct a chromosomal platform which can be utilized to insert/present new genes into a host organism's cell.

Production
Producing minichromosomes involves two primary methods, the de novo (bottom-up) and the top-down approach.

De novo
The minimum constituent parts of a chromosome (centromere, telomere and DNA replication sequences) are assembled

Top-down
This method utilizes the insertion of telomere sequences into existing chromosomes. This sequence signals for new telomeres which causes the truncation of the chromosome. The newly synthesized truncated chromosome can then be altered through the insertion of new genes for desired traits.

Role in Genetic Engineering
Unlike traditional methods of genetic engineering, minichromosomes can be used to transfer and express multiple sets of genes onto one engineered chromosome package Traditional methods which involve the insertion of novel genes into existing sequences may result in the disruption of endogenous genes and thus negatively affect the host cell. Additionally, with traditional gene insertion methods, scientists have had less ability to control where the newly inserted genes are located on the host cell chromosomes which makes it difficult to predict inheritance of multiple genes from generation to generation. Minichromosome technology allows for the stacking of genes side-by-side on the same chromosome thus reducing likelihood of segregation of novel traits.

Plants
In 2006, scientists demonstrated the successful use of telomere truncation in maize plants to produce minichromosomes that could be utilized as a platform for inserting genes into the plant genome In plants, the telomere sequence is conserved which implies this strategy can be utilized to successfully construction additional minichromosomes in other plant species

In 2007, scientists reported success in assembling minichromosomes in vitro using the de novo method

Other Organisms
Minichromosomes have been reported in yeast and animal cells. These minichromosomes were constructed using the De novo approach