To find out how many genes are contained in the genetic management of man, or genome, is not as simple as scientists thought. The very definition of a gene has changed since completion of the human genome project more than 15 years ago. Genes are typically defined as stretches of DNA that contain the instructions that are copied into RNA and subsequently into proteins. Scientists are still not quite agree as there are such protein-coding genes.
Estimates ranged from 19 to 21 901 306 — last count, which was published August 20 in BMC Biology.
How many human genes?
However, over the last decade, scientists have learned that not all genes make proteins. Many scientists have expanded the definition of the gene, to include the ones that make RNA, which, instead of turning into proteins performing other functions in the cell.
The inclusion of RNA-producing genes (also called coding genes is not) allowed to significantly increase the total number of genes, says Steven Salzberg, biostatistics from Johns Hopkins University, who led the new count. His team has already found more of these RNA genes — 25 of 525, including 18 484 long no coding RNA (IncRNA) genes than protein coding, and this count did not include the genes of miRNAs and other recently discovered small RNA. In addition to protein-coding genes, the human genome contains thousands of RNA genes, including transfer RNA (tRNA), ribosomal RNA, microRNA and other non-protein coding RNA sequences.
Even without the small RNA genes total count of human genes Salzberg has led to 46 of 831 at least. Other scientists dispute this assessment, and Salzberg notes that “wouldn’t be surprised if in ten years we never come to a single number.”
The number of human genes is not much greater than the number of genes in simpler organisms such as round worm Caenorhabditis elegans or the fly Drosophila melanogaster. This happens due to the fact that the human genome is widely represented alternative splicing. Alternative splicing yields several different protein chains from one gene. As a result of human proteome is much more of the proteome of the considered organisms. Most human genes have multiple exons, and introns are often much longer than the boundary of the exons in the gene.
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