Telomeres are DNA repeats at the ends of chromosomes. Their function is to maintain the integrity of chromosomes. Telomeres are shortened every time DNA is copied. Once telomeres are exhausted, chromosomes are prone to mutation, leading to arteriosclerosis or cancer. 
The study found that the length of a person's initial telomere DNA has been determined since birth, and there is great shame due to different people. The longest length can reach 20000 alkali plug pairs and the shortest is only 3000 base pairs
 some people speculate that the length of telomere DNA can be used to calculate people's life span.