There are an estimated 500,000 Alu repetitive DNA elements in the genome (chromosomes) of humans and other primate species. Most of the repeats have arisen in the evolutionary past (some 10 to 20 million years ago), others are still arising at new genomic sites; thus their total number keeps increasing. It is important to understand the mode of spreading of these Alu elements. The objective of this proposal is to establish if, and to what extent, Alu repeats are fixed or transient (polymorphic) in our genome; whether they arise in reversible or irreversible mechanisms. Polymorphism greatly complicates genetic analyses by blurring the distinction between meaningful and meaningless changes. The fixed or polymorphic state of a character is impossible to predict, it has to be established by analyzing large numbers of individuals. If the mode by which Alu repeats spread can be established as being irreversible, Alu's can be viewed as solid landmarks in the evolutionary dynamics of our genome and will become invaluable tools for phylogenetic analyses.
