[cheryl j (OP)]

This article from Science Daily says new genes spring from non coding DNA (although they also come from duplication and modification of existing genes.) I just wondered if this is what people refer to as "junk DNA"?

http://www.sciencedaily.com/releases/2014/01/140123142029.htm [Links inactive - To make links active and clickable, login or click here to register]

[CliffordK]

It is not surprising that mutations could lead to enabling or disabling non-coding DNA.  There have been questions why many organisms have so much non-coding DNA. 

Bacteria, of course, can sample environmental DNA, as well as exchanging plasmids.  Such ability to rapidly change could be very dangerous for more complex organisms.  However, the ability to slowly change and adapt is vital for the more complex organisms.  Thus, keeping a library of unused "code" would be reasonable, allowing slow evolution, without catastrophic rapid changes.   

[evan_au]

"Junk DNA" is DNA which has no purpose (that we have discovered yet...).

In the 1960s, it was thought that the purpose of DNA was to be transcribed into messenger RNA, which gets transcribed into proteins. This "protein-coding DNA" makes up around 2% of the human genome. That would make 98% "Junk".

Since the ENCODE project released its results in 2012, it seems that over 80% of human DNA is "conserved" (ie the DNA sequence is not changing randomly), which implies that it has some biological function, even if that function is not known to us at present.

Some functions for this DNA-previously-known-as-Junk include:

• RNA which regulates expression of DNA
  
• Structures which assist the replication of the cell's DNA, like centromeres & telomeres
  
• Spacers to help align genes during meiosis

If some randomly-changing section of DNA is suddenly transcribed in some individual, that could represent a new gene, although not necessarily a protein-coding gene.
See: http://en.wikipedia.org/wiki/Noncoding_DNA [Links inactive - To make links active and clickable, login or click here to register]