Scientists currently have no exact number for the amount of genes that humans have though the consensus is that it is anywhere between 20,000 and 25,000. With the question of how many genes there are in humans, several other issues come up. In order to count the number of genes we have, scientists must have a clear definition for the term “gene”. They must also locate these genes and have the tools and resources available to arrive at an accurate number. These issues make seeking an answer surprisingly difficult and time-consuming.
What is a Gene?
A simple definition of a gene is a sequence of DNA that can be used to create a protein. However, this definition is far too exclusionary as it does not acknowledge that some sections of our DNA code for RNA products and not proteins. Others code for nothing at all. These sections of DNA that do not result in the creation of proteins are called noncoding DNA and they make up about 99% of our genome. The frequency of these DNA sequences means that defining which among them should be considered genes is vital in the effort to approximate how many genes exist in humans. It is fairly clear that DNA sequences that result in any functional product should be considered genes but finding all of these sequences among the so-called “junk” is extremely difficult.
Where Are Genes?
Genes are not neatly located one after the other along the chromosomes. They are in seemingly random order and may have long stretches of DNA that do not contain genes in between them. These areas are referred to as “gene deserts” and not much is known about their biological functions. As a result of the issues in locating and counting genes, programs like RefSeq and GENCODE use multiple methods to determine and map the functional portions of the human genome.
