It is said that human genome contains over twenty five thousand genes, How many of these (can) express themselves as an external or internal trait in human beings (for e.g. like eye-colors, hair colors, earlobe-assosiation etc.). Other genes are responsible for (mostly) what functionalities?
The human genome doesn't contain 30000 genome, rather it contains 30000 genes, as the HGP has said us. Human gene is split gene,i.e., long sections of non-coding DNA is present in between short sections of actually coding DNA. Thus there is a lot of junk present. Different genes express themselves by a two step process, the first being transcription, where DNA is converted first into a mRNA, which undergoes splicing and then finally that mRNA is converted into protein and this is the second step which is known as translation. Thus it is by the conversion of DNA segment into proteins that helps the various genes in expressing themselves.
As for what the other genes do, not all genes are busy in determining phenotypic traits. There is a lot other things also going on.. the various biochemical reactions in our body need to be regulated by enzymes and the production of these enzymes are controlled by these genes. For more knowledge about this field... Google lac-operon concept or the tryptophan operon concept.