The human genome, which consists of all the DNA in all the human chromosomes, was found to have fewer genes than previously expected…again. As the human genome continues to be analyzed using new technologies, the estimated number of genes gets smaller and smaller. According to the most recent estimate in Human Molecular Genetics, there are only about 19,000 genes in the human genome. It was previously thought to be 26,000-30,000 in 2001 when the Human Genome Project information was initially used to estimate the total number of human genes. Previous to the Human Genome Project and modern genetic technology, the estimate for the number of human genes was one million, which was one gene for each protein.
The study was carried out at the Spanish National Cancer Research Centre and led by Alfonso Valencia, the Vice-Director of Basic Research and head of the Structural Computational Biology Group, and Michael Tress. In their study, they used proteomics methodology. Proteomics is a new field, and it is about studying ranges of proteins that exist in organisms. Whereas genetics is about genes and how they work, and genomics is about analyzing the entire human genome, proteomics is about analyzing the proteome, meaning collective mass of proteins in an organism or tissue.
In a study designed to learn about the number of genes in the human genome, the researchers carried out proteomics experiments that determined all the proteins in 50 tissue samples from humans. Since “genes code for proteins,” and proteins are produced as a result of gene expression, the total complement of proteins determined in the study indicated the totality of genes in the genome.
Different species have different sets and number of chromosomes, and each species has its own number of genes. The new estimate for humans separates them from mice by about 10 genes. Also, the new estimate for humans is lower than the estimate for worms (specifically the nematode Caenorhabditis elegans). An interesting finding in this study was that they did not find any proteins that were thought to exist in humans, but not in primates. In other words, there were no proteins that made humans distinct from primates. The implication is that there are no, or very few, extra human genes in the human genome compared to primates. What makes primates different from humans is, therefore, a big question.
Something that makes everyone scratch their heads are how this small number of genes can direct the development and life of such a complex things as a human (or any other animal or plant). Valencia was reported to say that, a few years ago, no one could have imagined that this small number of genes could make something so complex.
Recent developments in genetics have offered some ideas about what might be going on in the human genome besides genes coding for proteins. New insights into gene regulation have indicated how genes products are “edited” to modify the protein output from a gene and how small pieces of RNA change the gene regulation process. Epigenetics is the name of the new field that looks at how gene expression is varied by DNA activities that are “nearby” the genes. In the earlier days of molecular genetics (1960s to the 1990s), the DNA sequence in-between genes were called “junk” DNA because scientists did not know what this DNA did. With the evolution of epigenetics, geneticists are discovering some of the purposes of the junk DNA regions and the explanation for how complex human beings can only have 19,000 genes will likely emerge from this arena of research. The fact that the human genome was found to have fewer genes again should be seen as a helpful hint for directing researchers in their search to uncover a better understanding of human genetics.
By Margaret Lutze