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Telomeres and Longevity in Zebra Finches
from Smithsonian Magazine
A telomere is like an aglet. Aglets are those plastic or metal tubular thingies at the end of your shoe laces that keep the end of the shoelace from becoming frayed and facilitate inserting the lace into the eyelet. A telomere is a sequence of base pairs at the end of a chromosome.
A chromosome zips apart during cell division so that it can be replicated, and a small number of base pairs typically get lost during replication. This is because the molecular machinery that duplicates the chromosome can't read through to the end of the strand, so it just skips the last bit.
Any meaningful genetic information at the end of the chromosome would be lost or garbled. A nice long telomere at the end of the chromosome allows for multiple duplications without the loss of meaningful information, but over time even the telomere may be lost through attrition, and further replication of that chromosome would be a problem.