What goes on in that 3% it DNA, and what similarities do we share in the 97%?
In: Biology
The vast majority of the DNA is about how mammalian cells work. Brain, immune systems, the organs, etc. What’s left is the details, which are important but relatively not so much information.
Take a look at the skeleton of a dot or cat and you can identify many of the bones that match with the same bones in your own body. Sure, they’re different lengths, different shapes, but there a huge amount of correspondence.
Just because the DNA is the same doesn’t mean it’s used the same way. Different organisms share much of the same genes, but genes can be activated at different times or different amounts of proteins can be made from those same genes.
For example, both movie adaptations of Dune are based on the same book, but they are quite different.
Most genetics are the blueprints for really basic things, ( Ex. “housekeeping” genes that are necessary for basic cellular function, such as for replicating DNA, controlling the cell cycle, and helping cells divide) we share over half our genome with bananas for instance.
It’s [not really true](https://youtu.be/IbY122CSC5w) that we share certain percentages of DNA with various other organisms.
Also, most of our DNA codes for the basic mechanics of life that we all need, like enzymes and hormones and how to take apart glucose for energy. We have to have pretty much identical DNA for that stuff or we die.
Also, a lot of our body structure comes from [turning parts on and off](https://youtu.be/ydqReeTV_vk) instead of changing the DNA that codes for them. Remember thalidomide? Babies with perfectly good genes for arms and legs didn’t grow arms or legs because of non-genetic factors in their environment. There are a lot of ways to influence how a baby develops without changing its genes, though obviously those are also mostly uniform within a species because that commonality is what makes us a species and keeps us suitable for our environment.
So basically it doesn’t take changing a lot of genes to make a lot of change.
The short answer is “we don’t know what is going on in that 3% that causes different expressions of shared genetic traits”
But here’s a more fun one:
Humans are more than 60 percent identical to bananas. Many of the “housekeeping” genes that are necessary for basic cellular function, such as for replicating DNA, controlling the cell cycle, and helping cells divide are shared between many plants (including bananas) and animals.
Basically at the micro scale a lot of biological processes are the same or very similar in very different species and thus the DNA that provides the instructions for these processes are similar. Small micro changes to processes and structures can result in very large differences.
Another way of looking at it is: 2 water molecules contain 4 hydrogen atoms and 2 oxygen atoms and take the form of an incombustible liquid; however 2 diatomic hydrogen molecules and one diatomic oxygen molecule take the form of a highly flammable gas despite having the same subcomponents.
There’s also a lot of “junk” DNA that is inactive and doesn’t really control anything but still gets copied and passed on during reproduction.
How many limbs do we have? Vertebrate or invertebrate? Exoskeleton or soft skin? Scales, feathers hair or fur? Gills or lungs? Teeth or a beak? What about cell walls, or photosynthesis? Tail or no?
When you look at all of the possible variables across living organisms, or even just in the animal kingdom, it turns out that we answer almost all of these questions exactly the same way that Orangutans do. We actually AREN’T radically different, in the grand scheme of things.
Are we really that different?
Consider all the different forms of life on Earth. Compare a human to a mushroom, a tree, or a bacterium. Or even with a lizard, a bird, or a lion.
Then compare a human with an orangutan.
Differences aren’t just from the DNA being different, but from how the DNA is expressed – also called the phenotype.
Basically, we think of living organisms as having traits defined by their DNA, but really their traits are defined by *how their DNA is expressed*. There are a lot of ways this can vary from organism to organism. For example, your body may produce more or less of a protein based on a reaction to outside stimuli, and that protein could create different observable characteristics, but there is no change in the underlying DNA.
Identical twins (not fraternal twins), for example, usually have the same DNA. But they can have differences in how that DNA is expressed, which can result in differences in physical appearance, behavior, and even differences in health. Some of this can be caused by translation errors of the DNA (errors that result in the DNA being changed), but much of it will be caused by differences in environment that result in different biological responses.
When you reach a point where you actually *are* changing the underlying DNA, the changes start to become much more dramatic. This is why children can look so different from their parents (even though they often have some similar characteristics). By changing the DNA, even a small amount, you can make huge changes in the phenotype expression. Some of this can come from the fact that areas of DNA that weren’t used at all in one organism are now used by the new organism to produce proteins. These proteins don’t exist in the first organism, but could cause dramatic changes in appearance, behavior, or function in the new organism.
We share roughly [50% of our DNA with a parent, or a sibling](https://customercare.23andme.com/hc/en-us/articles/212170668-Average-Percent-DNA-Shared-Between-Relatives).
We share roughly [50% of our DNA with a banana](https://www.pfizer.com/news/articles/how_genetically_related_are_we_to_bananas).
We share roughly [99% of our DNA with a chimpanzee](https://www.amnh.org/exhibitions/permanent/human-origins/understanding-our-past/dna-comparing-humans-and-chimps).
We share, some of us, roughly [1.5% of our DNA with a Neanderthal](https://www.science.org/content/article/neanderthal-dna-you-carry-may-have-surprisingly-little-impact-your-looks-moods).
These “shared DNA” statistics are wildly inconsistent.
Unless we very carefully consider the different meanings what “shared DNA” is, with the very different meanings leading to wildly contradictory results, the phrase means nothing.
Considering that humans share 99.9% of their DNA with other humans, sharing 97% is quite a bit less.
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