Evolution and Functions of Telomeres

This chapter discusses the origin and evolution of telomeres, the basics of telomere metabolism and the way such structures impact cell function and organismal lifespan. Telomeres are typically constituted of short tandemly repeated sequences. A special type of telomeres is observed in drosophila and other insects, in which the telomere sequence is constituted of long, repeated stretches that span coding sequences. The chapter proposes transposon-mediated chromosome end healing as the original mechanism for telomere formation after linearization of the circular chromosome ancestor. In the prokaryote world, circular chromosomes are the rule and are considered as the primitive structure of all genetic material. Some types of higher order structures may exist (folding back structures, for instance), which may play a role in telomere functions. A major mechanism for telomere lengthening is telomerase activity, which adds telomere repeats to the overhangs of telomeres.