Final answer:
Alternative Lengthening Telomeres (ALT) is a mechanism used by cells to lengthen telomeric DNA, protecting the coding sequences of chromosomes during cell division.
Step-by-step explanation:
Alternative Lengthening Telomeres (ALT) is a mechanism used by cells to lengthen telomeric DNA by adding repetitive nucleotide sequences to the ends of eukaryotic chromosomes. Telomeres protect the coding sequences of chromosomes from being lost during cell division. Most somatic cells do not produce telomerase, an enzyme that adds nucleotides to telomeres, leading to telomere shortening and aging. However, some cells, known as ALT cells, utilize alternative mechanisms to lengthen telomeres without telomerase.