Over the past several decades, biologists have discovered, astoundingly, that we share 96%-98% of our DNA with chimpanzees, and over 90% with mice. These discoveries reveal something fascinating about the interconnectedness and shared origins of all life - although it also shows just how important the small number of different genes really are.
The genome is the full base of inherited information present in organisms of a single species, encoded into their DNA - the extraordinarily complex sequence of deoxyribonucleic acid housed in every cell, which contains all the instructions necessary to physically assemble a living body. All genomes, including the human genome, actually consist of a comparatively small active component of genes and a larger mass of inert, or "non-coding," material, which the theory of evolution tells us may be leftovers from millions of years of gradual adaptation. It is only in the past two decades that we have begun the task of sequencing our and other species's DNA. However, when scientists did so, they uncovered just how many genes our animals, and more specifically mammals, actually share.
Actually comparing the similarities between the human genome and other mammalian genomes is difficult because each species contains different numbers of genes, arrayed in different numbers of chromosomes. As a general rule, however, the Koshland Science Museum states that we share about 98% of our DNA with chimpanzees, and about 90% of it with mice. Dogs, says the National Geographic, fall somewhere in between. What this means is that when the genomes are compared side by side, more than 9 in every 10 genes will actually turn out to be the same.
It's not entirely surprising to find such large blocks of similar genes. After all, many of them will be encoding virtually identical structures. Mammals share basic skin, fur, and internal organs, including reproductive organs, at least in comparison to the quite different makeup of insects, reptiles, and other types of animals.
At the same time, it almost goes without saying that such comparisons should not be allowed to overstate the point: obviously, those genes which are not shared are extremely important. For instance, to use one of the examples above, chimpanzees have 24 chromosomes, although only a couple out of every hundred genes differ between humans and chimps. According to a Study in Nature, most of the actual differences between humans and chimps are not scattered randomly throughout our genetic code, but confined to some fairly narrow but highly significant segments of code that make up the major differences between our species and our genetically closest living relative. Overall, only a few percent of genes are believed to be highly active in coding the human body - so when these are the genes that differ, differences can take on disproportionate importance.