Genome rearrangements, resulting in variations in the numbers of copies of genes, occur when the cellular process that copies DNA during cell division stalls and then switches to a different genetic template, said researchers at Baylor College of Medicine in Houston in a report that appears today in the journal Cell.
The new mechanism is called replication Fork Stalling and Template Switching, said Dr. James R. Lupski, Cullen professor of molecular and human genetics and vice chair of the department at BCM. He is also professor of pediatrics. It not only represents a new way in which the genome generates DNA copy number variation, but it also demonstrates that copy number variation can occur at a different time point in the life of a cell. DNA replication takes place as the cell is dividing and becoming two.
Copy number variation involves structural changes in the human genome that result in the deletion or extra copies of genes (or parts of them). Often, this process is associated with disease, and also with evolution of the genome itself.
DNA (deoxyribonucleic acid) exists as two complementary strands that remain together because of the attraction between nucleotides. A or adenosine is always attracted to T (thymidine). C or cytosine is always attracted to G or guanine.
When a cell divides, it must reproduce its DNA so that each cell that results from the division has the same genetic code. That means it must replicate its DNA. During this process, an enzyme called a helicase separates the two strands, breaking the hydrogen bonds between the A T and G C base pairs holding the strands together. The two separating strands become the replication fork. On one strand, an enzyme called DNA polymerase reads the genetic material in the strand as a template and makes a strand (leading strand) of complementary DNA to pair to it. Again, the code is A to T and C to G. This process is continuous. On the other strand that comprises t
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Baylor College of Medicine