that portion of DNA that is not transcribed and expressed, comprising a major fraction of the base pairs of the human genome; much of this DNA is repetitive in seuqence and appears to serve no purpose; its function is not known. segments of DNA that appear to serve no function and are replicated along with the rest of the DNA that serves vital functions; examples are pseudogenes and tandemly repeated DNA sequences that seem functionless but are retained by unequal crossing-over. SYN: selfish DNA.