eli5: When scientists say that humans share a certain percentage of our genes with another species (chimpanzees, bananas, whatever), what actual genes do we have in common, or is that in the “we’restill figuring that out” part of science?
In: 0
Most of what we share is the nuts and bolts of being a living organism. For example, most animals have to share the same (or similar) genes for initiating cell division.
When scientists say that genes are “similar,” they really mean “these genes in humans have a similar counterpart in another organism.”
In that sense, it’s not shocking that we share 60% of our genes with bananas. You’d expect organisms with multiple cells to share a lot of the same basic machinery for making cell membranes and stuff.
No, it’s pretty much figured out. The genes are nothing more than sequences of a couple of basic chemicals, called nucleic bases, in order that varies from organism to organism, and from species to species. And the sequence is extremely super long, like billions of elements long. Add a couple of more chemicals to this sequence and you have the DNA.
Anyways, for many species, specific parts of sequences are similar. Very often, similarities reach more than 90%. That is what is meant by shared genes.
What confuses a lot of people is they think that genes=traits. It is kinda true, but not directly. Most of the gene sequences are garbage, they dont induce any protein creation. Other sequences, only trigger other portions of the gene chain, and these in turn encode certain types of proteins.
It’s a bit complicated. DNA are string of building blocks called nucleotides. To make it easier to work with the DNA, we can just replaced these building blocks by letter and them compared the strings of letters of the DNA between two species.
1) First we need to align the chains of letter to make them fit together. For example, if you have the chain of BCCDAABCD and the chain DAABCDCDDA you can see that the 6 first letter of the first chain and the 6 last letter of the second chain are the same, we can align them. Of course, the DNA is just one big long chain so it’s actually a bit more complex to do for real. There is usually a certain amount of letters that can’t be aligned with each other.
2) Then you need to spot the mutations that happened between those two DNA you are comparing. The first type of mutation is an Indel or an Insertion/Deletion. They form just one category because we can’t always know if a piece of DNA was deleted to one chain or it was inserted into the the one. So for example if you have DDACDABBADC and DDBDACDABBADC, you can see that there is a BD that was either deleted from the first chain or inserted in the second chain.
3) The next type of mutation is a substitution. That one is easy, if you have DDACDABBADC and DBACDABBADC, you can see that the second letter changed from D to B.
So now you end up with 4 categories when you compare two DNA. Identical, Substitution, Indel and Unaligned. Now you can just get a simply % of identical DNA, but the exact % will depend on you present the data. For example, you when you hear that our DNA is 98% similar to chimpanzee, it’s only when you look at substitution and ignore indel and unaligned DNA. If you count substitution and Indel, but not unaligned DNA you get a similarity of abut 95% and if you look at the entire DNA you get about 81% similarity.
Now when it come to knowing what those different actually are, it’s another story. Knowing what each building block of the DNA do is not something that we currently know. We identify what each bit of DNA do one by one over time, but it’s a very complex things. Some part of DNA doesn’t seem to do anything, but are they really useless or are we just not yet able to identify their role. There is billions of base pair in the human DNA, understand each of them will take a long long time.
Imagine DNA as a really long cookbook that tells us how to make the various parts of a body. This means that there are recipes in it that tell us how to make a lung or an eye or a blood cell directly from atoms. Now, in terms of basic composition and structures, almost all animals are made of the same parts, so their DNA would also contain the instructions need to make those cells. This means that if we compare the recipes in two given animal’s DNA, we are going to see a lot of identical or extremely similar parts. Since DNA is really just a long string of 4 different types of chemicals, we can really just compare the strings of DNA and determine which parts are similar.
Latest Answers