In geneticists at Arizona State University showed that individuals carrying more copies of AMY1 have more amylase in their saliva, thereby allowing them to digest more starch. The evolution of AMY1 thus appears to involve both the number of copies of the gene and the specific changes in its DNA sequence. Another famous example of dietary adaptation involves the gene for lactase LCT , an enzyme that allows mammals to digest the carbohydrate lactose, also known as milk sugar.
In most species, only nursing infants can process lactose. But around 9, years ago—very recently, in evolutionary terms—changes in the human genome produced versions of LCT that allowed adults to digest lactose. Modified LCT evolved independently in European and African populations, enabling carriers to digest milk from domesticated animals.
Today adult descendants of these ancient herders are much more likely to tolerate lactose in their diets than are adults from other parts of the world, including Asia and Latin America, many of whom are lactose-intolerant as a result of having the ancestral primate version of the gene.
LCT is not the only gene known to be evolving in humans right now. The chimp genome project identified 15 others in the process of shifting away from a version that was perfectly normal in our ape ancestors and that works fine in other mammals but, in that old form, is associated with diseases such as Alzheimer's and cancer in modern humans.
Several of these disorders afflict humans alone or occur at higher rates in humans than in other primates. Scientists are researching the functions of the genes involved in an attempt to establish why the ancestral versions of these genes became maladaptive in us. These studies could help medical practitioners identify those patients who have a higher chance of getting one of these life-threatening diseases, in hopes of helping them stave off illness.
The studies may also help researchers develop new treatments. When researchers examine the human genome for evidence of positive selection, the top candidates are frequently involved in immunity.
It is not surprising that evolution tinkers so much with these genes: in the absence of antibiotics and vaccines, the most likely obstacle to individuals passing along their genes would probably be a life-threatening infection that strikes before the end of their childbearing years.
Further accelerating the evolution of the immune system is the constant adaptation of pathogens to our defenses, leading to an evolutionary arms race between microbes and hosts.
Records of these struggles are left in our DNA. This is particularly true for retroviruses, such as HIV, that survive and propagate by inserting their genetic material into our genomes. Human DNA is littered with copies of these short retroviral genomes, many from viruses that caused diseases millions of years ago and that may no longer circulate. Over time the retroviral sequences accumulate random mutations just as any other sequence does, so that the different copies are similar but not identical.
By examining the amount of divergence among these copies, researchers can use molecular clock techniques to date the original retroviral infection.
The scars of these ancient infections are also visible in the host immune system genes that constantly adapt to fight the ever evolving retroviruses. PtERV1 is one such relic virus. Genetic evidence suggests that a PtERV1 epidemic plagued ancient chimps, gorillas and humans living in Africa about four million years ago.
Defeating one type of retrovirus does not necessarily guarantee continued success against others, however. This finding is helping researchers to understand why HIV infection leads to AIDS in humans but less frequently does so in nonhuman primates. Clearly, evolution can take one step forward and two steps back. Sometimes scientific research feels the same way.
We have identified many exciting candidates for explaining the genetic basis of distinctive human traits. In most cases, though, we know only the basics about the function of these genome sequences. These rapidly evolving sequences do point to a way forward.
The story of what made us human is probably not going to focus on changes in our protein building blocks but rather on how evolution assembled these blocks in new ways by changing when and where in the body different genes turn on and off. Experimental and computational studies now under way in thousands of labs around the world promise to elucidate what is going on in the It is looking less and less like junk every day.
Diversifying our cataloging and curation of human genome sequences, Lee argues, will help us better understand the genomic tapestry that makes up our species. For example, researchers now know that human genomes differ from one another by about 0. So, modern genomic science is increasing our appreciation of the uniqueness of the genetic blueprints that build wonderfully individual human beings.
At the same time, cutting-edge research is reinforcing the fact that we humans share a remarkable similarity in our DNA. What we do with this knowledge is extremely important.
DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Mitochondria are structures within cells that convert the energy from food into a form that cells can use. Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.
Each base is also attached to a sugar molecule and a phosphate molecule. And as we continue to sequence ,, million, or all seven billion people on the planet, we will find a lot more variation. This means that humans have many more differences than we first thought. Imagine that your DNA is a car. There are certain obvious variants you can have: blue or white, two-door or four-door, convertible or sedan. These changes represent the 0. Because the other In other words, what we believe is static may actually be variable.
More than 0. With the rise of services that offer to sequence your DNA , more and more people are talking about the value of personal genomics and what you might uncover about yourself. But those examples of straight-forward, visible evidence are just starting points in the immense and only partially explored field of personal genomics.
Because our data is limited by the amount of sequenced DNA available for study, scientists like myself have only explored a small portion of the genetic variation that exists in the world.
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