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Unusual chromosomes and their properties
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Types of artificial chromosomes

HAC – Human artificial chromosome

Human artificial chromosome was constructed from scratch during the 1990s in human fibrosarcoma cell line (fibrous connective tissue containing tumor). This was accomplished by adding alpha-satellite DNA to telomeric and genomic DNA, which resulted in a completely new 47th microchromosome. Its length can go up to 10,000 kb (including the inserted DNA of interest) making it smaller than half of regular human chromosomes (out of haploid chromosome number – 23).

The good thing about human artificial chromosome is that it is completely independent. Unlike yeast and bacterial artificial chromosomes which are based on plasmids and integrate themselves into the genome, human artificial chromosome is constructed de novo, with all the regular parts of a chromosome (centromeres, telomeres, etc.). This means that it won’t disrupt the existing genetic material when inserted in the cell, which is important since YACs are the least stable, while BACs are also less stable than HACs, as their integration can lead to unpredictable expression levels or some other problems when the host cell’s genome is interrupted with their DNA.

Scientists are creating HACs in two ways. One of them is de novo, but it poses some problems because making a chromosome from scratch has some limitations – some specific elements like centromeres might not be constructed correctly, or some DNA fragments might not successfully integrate into them.

Another way of creating HACs is by using one already present normal human chromosome. Namely, existing chromosome is modified by cutting off some of its parts, and then some additional DNA is added at some specific sites (also known as Cre-Lox recombination).

Human artificial chromosomes can be used for a number of different things; for example, as gene transfer vectors in expression studies, for determining the function of human chromosomes, for annotating of the human genome, or for doing some specific things in the cell by carrying additional specific genes that would help in fighting some diseases, for example.
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RE: Unusual chromosomes and their properties - by zemaxe7 - 05-02-2014, 02:21 PM



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