Why are non-coding genes called "genes"

[instantresults]

I thought that a gene by definition is a unit of heredity, so a portion of DNA that doesn't code for anything wouldn't be a unit of heredity and therefore shouldn't really be called a gene, no? Also if current estimates for protein coding genes in human genome is about 20000, how many total genes are there in human genome?
thanks for any help

 

[BillTre]

Genes don't have to code for any thing to be a gene.
Gene is a term that has been used since before DNA was understood. It has been used to designate any inheritable trait.

Non-coding control sequences can be found as mutations (and therefore considered a gene) even though they do not code for proteins or RNA transcripts.
They could be binding sites for proteins which could control transcribing of a neighboring coding sequence.