There’re about 20,000 protein coding genes in human. They’re strictly regulated though. Some are active everywhere and all the time, while some are active only at certain parts of our body, or only at certain age.
Long before we sequence the genome people used to think we’d have 100,000 genes because our genome is that much bigger than a sea sponge or ‘lesser’ animal.
So how do we get to be so complex with just 20,000 genes? Well, each gene is broken up into parts called “exons”, when exons are put together it forms a “transcript” By mixing and matching exons you can make many different transcripts from 1 gene. Humans have about 100,000 different protein coding transcripts, even thought we only have 20,000 genes.
Another great question by Viking10 🙂 Others have already answered that about 20,000 protein coding genes are present in human genome.
I would like to approach your question a bit differently because you mentioned “in our body”. As there are our own cells in our body, there are also microbial cells. Did you know that there are a lot more microbial genes in our bodies compared to the genes from our own genome? There are an estimate of 2 million microbial genes in our bodies compared to the 20,000 human genes according to the lecture of Dr. Martin Blaser, author of the Missing Microbes. This is really interesting, as we do not usually think about the helpful bacteria that live with us, attached to us. And they are not just in our intestines, they are everywhere in our body.
There is an interesting paper called “The Human Microbiome: Our Second Genome”. In this paper they mention that 90% of the total number of cells associated with our bodies are from microbes and only the remaining 10% are human cells.
All of these answers are so great and interesting! I’ll try an take a difference approach as well to add to the information. While all the cells in your body are carrying the same genetic information, as in the DNA nucleotide sequences we inherit from our parents or the “blueprint”, different cells are expressing, or turning “on”, different sets of genes. That’s why your blood, liver, bone, and neuronal cells can be so different. They are building different parts of the blueprint! Additionally, neuronal cells are turning genes on or off dependent on your experiences!