In a new research, scientists have found the number of protein generating genes in humans to be 19,000 - 1,700 fewer than the most recent annotation and well below the initial estimations of 100,000 genes.

The study says that almost all of these genes have ancestors prior to the appearance of primates 50 million years ago.

"I call it the shrinking human genome. The coding part of the genome (which produces proteins) is constantly moving. No one could have imagined a few years ago that such a small number of genes could make something so complex," explained Alfonso Valencia, vice director of basic research at the Spanish National Cancer Research Centre (CNIO).

In order to determine a map of human proteins, the researchers integrated data from seven large-scale mass spectrometry studies - from more than 50 human tissues - "in order to verify which genes really do produce proteins."

They analysed thousands of genes that were annotated in the human genome, but that did not appear in the proteomics analysis - the most powerful tool to detect protein molecules.

"1,700 of the genes that are supposed to produce proteins almost certainly do not for various reasons, either because they do not exhibit any protein coding features, or because the conservation of their reading frames does not support protein coding ability," informed Michael Tress, a researcher at the CNIO's structural computational biology group.

According to the findings, more than 90 percent of human genes produce proteins that originated in metazoans or multicellular organisms of the animal kingdom hundreds of millions of years ago.

The figure, however, is over 99 percent for those genes whose origin pre-dates the emergence of primates 50 million years ago.

"It indicates that the differences between humans and primates at the level of genes and proteins are very small," researchers noted in a paper published in the journal Human Molecular Genetics.