Question

For a given Short Tandem Repeat, what is the same about it for all individuals within a population? How can it vary between individuals?

Answer 1

Short Tandem Repeats (STRs) are short sequences of DNA which consist of a two to thirteen nucleotides repeated hundreds of times in a row on the DNA strand. For e.g., in a 16 bp sequence of "gatagatagatagata" there are 4 copies of the tetramer "gata". The Variations in DNA sequences between individuals are termed as "polymorphisms". The polymorphisms in STRs are due to the different number of copies of the repeat element that can occur in a population of individuals. In STR analysis, the exact number of repeating units in measured in individuals. Unrelated people almost certainly have different numbers of repeat units, hence STRs can be used to discriminate between unrelated individuals.