Unique or single copy genes

The DNA in the human genome can be usefully classified into lengths of unique or single copy genes. The function of these genes is well known.

Some sections of DNA do not code for proteins

There are also so called Highly repetitive sequences. The function of these sequences is not known.

Highly repetitive DNA used to be called Junk DNA as we could not find a use associated with it. However new ideas have speculated that it may be that these sequences may have had a function earlier in the evolution of the organisms or may have on later in evolution.

Some of these sequences can be used in DNA profiling as they are often unique to an individual.

The number of times certain tandem repeats occur is a useful marker between individuals.

Use of nucleotides containing dideoxyribonucleic acid to stop DNA replication in preparation of samples for base sequencing. So called tandem repeats are often highlighted using artificial DNA replication controlled by dideoxyribonucleic acid nucleotides.

Telomeres

These are highly repetitive DNA sequences at the end of chromosomes which protect them and prevent incomplete replication.