Some made changes to vast stretches of the genome, seemingly devoid of meaning.
Some made changes to vast stretches of the genome, seemingly devoid of meaning.
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Essay numbersMutantsArmand Marie LeroyWe are all mutants, but some of us are more than others, – says geneticist A. Leroy, an expert in the field of evolutionary biology and author of many wonderful popular science books.
Journal siteHow to buy
Armand Marie Leroy”Ecology and Life” No. 7-8, 2009
The book “Mutants. On the Form, Variability and Errors of the Human Body ”is just getting ready for publication in Russian. Its author, Armand Marie Leroi, is known not only as a geneticist, an expert in the field of evolutionary biology, but also as the author of wonderful popular science books. The son of a Dutch diplomat, he was born in 1964 in New Zealand. Studied at Dalhousie University (Canada); in 1993 he received his doctorate in ecology and evolutionary biology from the University of California (USA). In 2001, he was awarded the Times-Novartis Scientist of the New Century medal, and in 2004, the Guardian newspaper’s first book prize. He currently lives in London and lectures on evolutionary developmental biology with great success. And he writes new books, devoting a significant part of his time to the cause of scientific popularization.
Our bodies (and I add with some hesitation – our souls) are the products of our genes. At the very least, our genes contain the information – one might say technical instructions – that allows embryonic cells to transform into different parts of our body. But behind this seemingly simple answer hides a whole world about which we know little. Genetics, in the words of one popular writer on similar topics, is language. “It has its own vocabulary — the genes themselves, grammar — a way of organizing hereditary information, and literature — the thousands of instructions needed to create a human being.” This is all true. But he forgot to mention one thing: the language of genes is largely inaccessible to us.
On February 15, 2001, an international consortium of scientists announced the complete or almost complete sequencing of the human genome. We are told we have about 30,000 genes. But even geneticists are at a loss for much of the content of the genome. When viewing it here and there, they come across “words” with a fairly clear meaning. The meaning of other “words” can be guessed, because they are closely related to familiar ones. Some of the “grammatical patterns”, “syntactic rules” by which genes combine to give meaning to their “utterances” are also understandable. But the “syntax” of genes is much more complex, subtle, and more varied than any of the languages spoken by humans. And although it cannot be said that all this “literature” is a closed book for us, we are just beginning to read it.
And it’s not that we don’t know how to decode the genome. The experiments that try to do this usually involve engineering the embryos – either by surgically adding or removing organs, or adding or removing genes. Of course, embryos always belong to animals: newts, frogs, chickens or mice. They tell us quite a lot about ourselves, because it just so happens that the genetic “grammar” of all living things is very similar. But just as the vocabulary and grammatical rules of human languages have drifted more or less away from each other over time, so have the “languages” of genes. To learn only from animals is to run the risk of being wrong, as Leonardo da Vinci did when he sketched a human fetus attached to what was certainly a cow’s placenta. Finally, we need some direct paths leading to the human genome and to the human body.
Cleopatra, according to one historical source, ordered to open the stomachs of pregnant slaves in order to observe the development of their embryos. Given her curiosity and her ability to find time for laboratory work in the tense rhythm of social commitment, we can hardly follow her example. We must find more careful ways to study the human body. We need to find … mutants.
* * *
…Francis Bacon (1561–1626), in his 1620 Novum organum, began to classify natural history. There are, he says, three types of natural history, which “deal either with the freedom of nature, or with the errors of nature, or with the bonds of nature; so we can make a good distinction between birth history, extraordinary birth history and art history, the latter we also often call mechanical and experimental art. ” In other words, natural history can be divided into the study of normal nature, aberrant (deviating from the norm) nature, and nature that is influenced by humans. Bacon also points out how to start the second part of his program: “We must create a collection or a special natural history of all freaks and wonderful works of nature, which will include every innovation, rarity or anomaly.” Of course, Bacon is interested in collecting aberrant objects not for their own sake, but in order to understand the reasons for their originality. He is a philosopher, and he has a desire to know the nature of things. We must, he says, study cases of deviation from the norm, “for when nature is known in its variations and the reasons for them become clear, it will not be difficult by art to achieve from nature what it achieves by chance.” Centuries ahead of his time, Bacon admits that the search for the causes of errors is not an end in itself, but only a means. Ugly, strange, deviating, or simply different, he says, reveals the laws of nature. And when we learn these laws, we will be able to reconstruct the world at will.
…Bacon’s command that we should collect what he calls “extraordinary births” may seem unpleasant. Our deliberate, often ostentatious love for human diversity quickly dries up when diversity turns into ugliness. And yet, activity should not be confused with a goal. What were “monsters” and “extraordinary births” to Bacon are just part of the spectrum of human forms for us. Over the past twenty years, this spectrum has been examined and studied as never before. All over the world, people with physiological or physiognomic characteristics that differ in one way or another from the usual, were subjected to registration, photographing and clarification of genealogies. They were found in Botswana and Brazil, Baltimore and Berlin. Blood samples were taken from their veins and sent to laboratories for analysis. Their biographies, anonymous and reduced to simple biological facts, filled scientific journals. They have become, hardly knowing about that, the starting material for a grandiose biomedical enterprise, perhaps the greatest in our century, in which tens of thousands of scientists are collectively involved and whose goal is nothing more than an explanation of the laws of development of the human body.
Most of these people have mutations, that is, defects in some genes. Mutations occur due to errors in DNA copying or repairing mechanisms. To date, mutations that make some of us look, feel, or behave differently from nearly everyone else have been found in over a thousand genes. Some of these mutations destroy or, conversely, add whole chunks of chromosomes to existing ones. Others affect only one nucleotide – a structural unit of DNA. The physical nature and degree of the mutation, however, are not as important as its consequences. Hereditary diseases are caused by mutations that alter the gene sequence of DNA, so that the protein encoded by it takes on different, often defective, forms or is not produced at all. Mutations change the “meaning” of genes.
Changing the meaning of one gene can have extremely far-reaching consequences for the genetic “grammar” of an organism. There is a mutation that will make you red-haired and fat. The other will cause partial albinism, deafness, and fatal constipation. Another will provide you with short fingers and toes and malformed genitals. By changing the meaning of genes, mutations make us think about what these genes are for the body in the first place. Taken together, they are like a scalpel that cuts into the structure of the genetic “grammar” and exposes its logic.
Interpreting the meaning of mutations will require the use of reverse logic (counter-logic), which is, to begin with, the opposite of intuition. If a mutation causes a child to be born without arms, then while it might be tempting to talk about the gene for “no hands,” the mutation is in fact evidence of a gene that helps ensure that most people have hands. This is because most mutations destroy meaning. In the language of genetics, these are “loss of function” mutations. A minority of mutations add “meaning” and they are called “function acquisition” mutations.
When interpreting the meaning of a mutation, it is important to know which one we are dealing with. One way is to find out how they are inherited. Loss of function mutations are usually recessive: they only affect a child’s body when defective copies of a gene are inherited from both parents. Mutations in “function acquisition” tend to dominate: a child needs only one copy of the gene to produce the desired effect. While this distinction cannot be considered definitive (some dominantly inherited mutations result in loss of function), it provides a good initial orientation. Whether gaining or losing, both types of mutations tell something about the function of the genes they affect and thus explain a small part of the genetic “grammar.” Mutations allow the body to be deconstructed.
…Who are mutants after all? To say that the sequence of a given gene has a mutation, or to call the carrier of such a gene a mutant, is to give a rather offensive characteristic, which implies at least a deviation from a certain perfection, an ideal. Yet people differ from one another in a great many ways, and these differences are, at least in part, inherited.
Which of us has a genome of genomes – the same by which all other genomes will be judged? There is a short answer to this question: no one. The human genome whose sequence was published on February 15, 2001 is not a standard. It is simply a combination of the genomes of an unknown number of unknown people. As such, it makes no claim to conformity or excellence (and the scholars who supported and implemented this great project never made such claims). And chance in no way diminishes the value of a given genomic sequence. After all, the genomes of any two people are 99.9% identical. On the other hand, a genome of nearly three billion base pairs suggests that there is a difference of several million base pairs between any two people. Interest lies in these differences.
If an ideal or normal genome does not exist, then can we find these qualities in a single gene? Maybe. All of our 30,000 genes show at least some diversity. For the most recent generation of the inhabitants of the Earth, mutations occurred on average 240 times in each base pair of the human genome. Not all of these mutations altered the “meaning” of genes or affected them at all. Some made changes to vast stretches of the genome, seemingly devoid of meaning. Not containing genes that would contribute to the “grammatical” structure of the body, these areas are subject to mutations again and again. The “scalpel” does its job, but without consequences for the human body or mind. Other mutations affect the coding regions of genes without actually altering the sequence of the proteins they code. They also remain silent.
Of all the mutations that change the meaning of genes, a small part of them will be beneficial for the body, and over time, these mutations will become more frequent. So frequent that it would hardly be fair to call them mutations at all. They are called “variants”, or, more scientifically, “allelic forms of genes” (“polymorphisms”). In Africa, the frequency of the D32 allele of the CCR5 gene is currently increasing, since it contributes to the body’s resistance to the human immunodeficiency virus and, accordingly, to AIDS. This is a new phenomenon, however, many polymorphic genes were acquired in antiquity. They are the material that makes up the diversity of humanity. They give us differences in skin color, height, weight, and thesis synthesis facial features; they also certainly determine, at least in part, our differences in temperament, intelligence, bad habits. They can cause illness, but for the most part, diseases of old age, such as senile dementia and heart attacks.
How common must a mutation be before it becomes polymorphism? The answer to this question is somewhat arbitrary, but it is believed that if the changed sequence meets with a global frequency of 1% or more, then it could not cause much harm in its history, but, on the contrary, could even be beneficial for its carriers. According to this criterion, at least one polymorphism is found in about 65% of human genes studied for this subject.
Some genes have dozens of them. This diversity should not overwhelm us. Most human genes have only one variant, which is much more common than the rest, and therefore it is quite reasonable to speak of this variant as normal, if only in a statistical sense.
The problem of the ideal is much more complicated.
