Now it’s anniversary of human’s genome sequencing, so check Science’s web page for some info. I think the current number is about 24 000 genes.
The one with least genes would be probably some small virus 🙂

I’m interested in that "2 or 3 different jobs", do you have some furthwer info?

Human genome has about 23,000 genes. As JackBean said, viruses have the least number of genes in their genomes. And the one with most genes is a zooplankton, Daphnia pulex, with 31,000 genes; according to this news: http://www.physorg.com/news/2011-02-cru … enced.html. The record for the most genes can change in the course of time as new genome projects are conducted.

Some genes’ primer transcripts can be spliced in alternative ways. So, one gene may lead production of different mature mRNAs and so that more than one polypeptide. Also, a polypeptide product of one gene can work in different multimer proteins which are consisted by two or more polypeptides. These are the reasons why one gene may have more than one task.

the completion of the Human Genome Project was celebrated in April 2003 and sequencing of the human chromosomes is essentially "finished," the exact number of genes encoded by the genome is still unknown. October 2004 findings from The International Human Genome Sequencing Consortium, led in the United States by the National Human Genome Research Institute (NHGRI) and the Department of Energy (DOE), reduce the estimated number of human protein-coding genes from 35,000 to only 20,000-25,000, a surprisingly low number for our species (7). Consortium researchers have confirmed the existence of 19,599 protein-coding genes in the human genome and identified another 2,188 DNA segments that are predicted to be protein-coding genes.

In 2003, estimates from gene-prediction programs suggested there might be 24,500 or fewer protein-coding genes (1). The Ensembl genome-annotation system estimates them at 23,299.