Transfer of genes through generations. Hereditary traits are passed on from generation to generation using genes. How many generations do it take for twins to be born when passed from woman to woman?

Scientists believe that intellectual abilities are determined by 50–70% by genes, and the choice of profession by 40%. 34% of us have a tendency towards politeness and rude behavior. Even the desire to sit for a long time in front of the TV is 45% a genetic predisposition. The rest, according to experts, is determined by upbringing, social environment and sudden blows of fate - for example, illness.

A gene, just like an individual organism, is subject to the action of natural selection. If, for example, it allows a person to survive in harsher climatic conditions or withstand physical stress longer, it will spread. If, on the contrary, it ensures the appearance of some harmful trait, then the prevalence of such a gene in the population will fall.

During the intrauterine development of a child, this influence of natural selection on individual genes can manifest itself in quite strange ways. For example, genes inherited from the father are “interested” in the rapid growth of the fetus - since the father’s body obviously does not lose from this, and the child grows faster. Maternal genes, on the other hand, promote slower development - which ultimately takes longer, but leaves the mother more strength.

Prader-Willi syndrome is an example of what happens when the mother's genes “victory”. During pregnancy, the fetus is inactive; After birth, the child experiences developmental delay, a tendency toward obesity, short stature, drowsiness, and impaired coordination of movements. It may seem strange that these apparently unfavorable traits are encoded by maternal genes - but it must be remembered that normally these same genes compete with paternal genes.

In turn, the “victory” of paternal genes leads to the development of another disease: Angelman syndrome. In this case, the child develops hyperactivity, often epilepsy and delayed speech development. Sometimes the patient’s vocabulary is limited to just a few words, and even in this case the child understands most of what is said to him - it is the ability to express his thoughts that suffers.

Of course, it’s impossible to predict a child’s appearance. But we can say with a certain degree of confidence what the main features will be. Dominant (strong) and recessive (weak) genes will help us with this.

For each of its external and internal characteristics, the child receives two genes. These genes can be the same (tall, full lips) or different (tall and short, plump and thin). If the genes match, there will be no contradictions, and the child will inherit plump lips and tall height. In another case, the strongest gene wins.

A strong gene is called dominant, and a weak gene is called recessive. Strong genes in humans include dark and curly hair; baldness in men; brown or green eyes; normally pigmented skin. Recessive traits include blue eyes, straight, blond or red hair, and lack of skin pigment.

When a strong and a weak gene meet, as a rule, the stronger one wins. For example, mom is a brown-eyed brunette, and dad is blond with blue eyes, with a high degree of probability we can say that the baby will be born with dark hair and brown eyes.

True, brown-eyed parents may give birth to a newborn with blue eyes. Thus, genes received from a grandmother or grandfather could have an effect. The opposite situation is also possible. The explanation is that it turns out that for any trait we have, it is not just one gene from each parent, as was previously believed, that is responsible, but a whole group of genes. And sometimes one gene is responsible for several functions at once. So a whole series of genes are responsible for eye color, which are combined differently each time.

Hereditary diseases transmitted by genes

A baby can inherit from his parents not only appearance and character traits, but also diseases (cardiovascular, cancer, diabetes, Alzheimer's and Parkinson's diseases).

The disease may not appear if basic safety measures are taken. Tell your gynecologist in detail about serious health problems not only for you and your husband, but also for your close relatives. This will help protect the baby in the future. Sometimes absolutely healthy parents give birth to a baby with a hereditary disease. It was embedded in the genes and appeared only in the child. This usually happens when both parents have the same disease in their genes. Therefore, if you are planning a child, according to experts, it is better to undergo a genetic examination. This is especially true for families in which children with hereditary diseases have already been born.

A weak gene may not be detected for one or many generations until two recessive genes from each parent occur. And then, for example, such a rare symptom as albinism may appear.

Chromosomes are also responsible for the sex of the child. For a woman, the chances of giving birth to a girl or a boy are equal. The gender of the child depends only on the father. If an egg meets a sperm with sex chromosome X, it will be a girl. If U, a boy will be born.

What else may depend on genes:

Gender – 100%;

Height – 80% (for men) and 70% (for women);

Blood pressure – 45%;

Snoring – 42%;

Female infidelity – 41%;

Spirituality – 40%;

Religiosity – 10%.

There are also genes responsible for the development of certain conditions, such as depression or a tendency to uncontrollable eating.

The level of mutations in men is 2 times higher than that in women. Thus, it turns out that humanity owes its progress to men.

All representatives of the human race are 99.9% identical in DNA, which completely rejects any basis for racism.

Hello, dear readers of my blog! Most often, women who are concerned about the birth and upbringing of twins turn to me for advice. Some people dream of their “Hansel and Gretel”, while others are afraid of their appearance like fire. I'll try to help both. Let me tell you about your likelihood of having twins? I will reveal all the secrets of conceiving two babies at once.

The story of twins begins the same as for all other children - with the fertilization of an egg by a sperm. Immediately after this, miracles begin. Depending on whether these miracles happen with one egg or several, they are born.

Modern science defines three types - monozygotic (identical), dizygotic and mixed type - polar twins. There are also Siamese twins and other options. But now we are talking about cases where everything is within the norm.

If the zygote is divided into several parts, the result is monozygotic twins with the same genotype. These are always children of the same sex, precisely those about whom programs are often filmed and research is conducted. After all, they are like two drops of water similar to each other. They have similar characters and even the facts of life often coincide.

The later the zygote splits, the more likely it is that the babies will be “” - one is right-handed, the other is left-handed, one has a birthmark on the left, the other has a birthmark in the same place on the right, etc.

If a mother carries two zygotes, the twins are born with different genotypes. They differ from ordinary brothers and sisters only in that they come into this world during the same birth. Interestingly, fertilization of these eggs can occur at different times. Not necessarily during one sexual act. Sometimes such twins are even born from different fathers!

Unlike the other two types, polar twins are only twins. They inherit identical genes from their mother and different genes from their father. The beautiful concept of “royal twins” refers to just such a polar type, when a boy and a girl are born, outwardly completely similar to each other.

Probability of twins as a gift from ancestors

The occurrence of twins is influenced by several factors, in determining which science relies, for the most part, on statistics. Let's start with the natural, or more precisely, genetic factor, which plays a role even on the scale of civilizations.

We are talking about dizygotic twins, because multiple births can be inherited, and not the ability of the egg to divide. Representatives of the Negroid race are born with twins more often than others. The next most common births are Europeans, but in Latin America or Japan the birth of twins is very rare.

Science has clearly determined through which line multiple births are transmitted. The likelihood of twins is greater if one or both parents have already had twins. In this case, the gene for multiple births is transmitted through the female line.

Let me explain. If in your family your parents (grandmothers, great-grandmothers) or their cousins ​​have already had twins, then you are in the probability zone.

Through the male line, transmission of the desired gene is possible through a generation. If a man is one of the twins, then he can, theoretically, become a transmission link between his mother and his daughter. However, the appearance of twins will be influenced not by his gender, but by the heredity of his wife.

Natural factors of multiple births

In addition to heredity, age is of great importance. The older a woman is (after 30 and before 40-45 years), the greater the likelihood that she will become the mother of twins. This is due to a potential increase in the production of the hormone responsible for the functioning of the sex glands and influencing the formation of ovarian follicles.

Hormones are also produced in greater quantities in the summer - during longer daylight hours. Therefore, it is believed that the summer period is the best time for conceiving twins!

Another natural factor is the health of the expectant mother. The body controls the balance between a woman's capabilities and the load on her during pregnancy. The probability of twins is:

• if a woman eats well and is in excellent physical shape;
• perhaps more complete than fashion magazines demand of her.

The body also becomes stronger, becoming more active with each new birth. The chance of having twins increases if you already have children.

Artificial "probability" of twins

Artificial factors for multiple births include hormonal therapy. After stopping long-term use of oral contraceptives, the woman’s body happily restores the functions of conception. Hence the likelihood of multiple births.

It also increases if hormonal infertility treatment is carried out, aimed at stimulating ovulation. I’m not even talking about artificial insemination (IVF), in which several embryos are implanted into a woman’s uterus. The probability of twins is high.

The fact that the production of hormones can be stimulated does not mean that by taking hormonal drugs you can purposefully influence the number of your future children. This effect is possible only as a side effect of treatment prescribed by a doctor. Independently choosing and taking such drugs can cause irreparable damage to your health!

It’s impossible to predict, what to do?

Even taking into account all natural and artificial factors, their gestation, birth and future life will be under the supervision of doctors and scientists around the world for a long time.

We cannot calculate the number of children before conception and influence this number before conception - we also cannot. Did you inherit the “twin gene” from your ancestors or not? Are you a slim woman or a plump one? If you are going to become a mother, accept the fact that nature will choose for you. Trust me, as a mother of twins. Any number of children is only for the better!

Healthy babies to you! Don't forget to subscribe to the blog and leave your comments! See you again!

10.01.2009, 21:19

Good day, colleagues! I have a theoretical question (I just don’t know geneticists, but it’s very interesting). After how many generations does genetic information “dilute” so much that it is impossible to determine a relationship using DNA analysis?

12.01.2009, 09:38

Hello!
A theoretical question can only be answered theoretically ;).
A lot depends on who the relationship is established between. And also on whether there is an undoubted relative of at least one of those being checked.
Theoretically, mitochondrial DNA and the Y chromosome are quite stable and there are few spontaneous changes in them. A person always receives mitochondria only from their mother (without dilution :)). The chromosome goes through the male line.

Perhaps a specific example will be clearer.

12.01.2009, 21:20

Thanks for the answer! As far as I understand, such an example arose (theoretical: ah:) let’s take a real person, for example, Prince Vladimir, who died in 1015 and had a dozen or two children :). Let's say that in our time a person is trying to prove that he is a descendant of Vladimir, is it even possible to do this, and if so, what is the percentage of accuracy. And if I understood correctly and in some generation there were only girls, then it is impossible to establish the “paternity” of Vladimir (the chromosome has been lost)?

13.01.2009, 13:00

Do we have a DNA sample of Prince Vladimir;)?

If we theorize weight, then the example is complex. Since about a thousand years have passed, the likelihood of spontaneous changes accumulating is high. And as you correctly noted, the probability of losing the prince’s chromosome is high.
In this case, it would be necessary to use 2 markers, the Y chromosome and an autosomal marker (so-called satellite DNA). Under favorable circumstances, determination of kinship is possible.

13.01.2009, 22:53

The relics of Vladimir are in the Kiev Pechersk Lavra:ad:
If I understood everything correctly, then it is almost impossible for modern Petya, who claims that he is a descendant of Prince Vladimir, even with DNA, to prove his relationship after a thousand years (we don’t know what happened to this family over a thousand years). Thank you for your answer and attempt to explain to a layman in genetics (I had to remember the medical institute). :ah:

31.07.2009, 11:38

In my opinion, the meaning of the question was different - after how many generations will there not be the slightest information about the human genes left in the chromosomes of the descendants of a particular person? If a child, relatively speaking, has half the genes of the parent, then the grandson has a quarter, the great-grandson has one eighth, after 17 generations less than one hundred thousandth, after 31 generations less than one three billionth. If there are no more than 100,000 genes (3 billion nucleotides) in human DNA, and in a hundred years there are about five generations, then in about 400 years not a single gene from a particular person will be preserved, and after another 400 years not even a single nucleotide will remain?

31.07.2009, 11:51

spbivan, You are thinking completely wrong. What is the purpose of your participation in this topic?

31.07.2009, 15:22

I understand that I am reasoning incorrectly, but my goal, like that of the author of this topic, is to get an answer to the theoretical question posed initially, because it is interesting to me. At the same time, I would like to understand what is wrong in my reasoning. If a male chromosome is passed on from father to son, then, apparently, even after many generations the connection can be traced. After how many generations is the maximum with a probability of at least 80-90%? And if a man alternates female and male descendants in a random order, then after how many generations, at most, nothing will remain of his specific genes with a probability of 80-90%? Can genes be passed on forever with a good probability or not? What is at least the order of the number of generations on average?

31.07.2009, 22:29

“Genes persist” for quite a few generations.
Unfortunately, I cannot answer your question in more detail. If you have a practical question, please contact us.

03.08.2009, 16:07

03.08.2009, 21:26

And yet this is not a practical question, but a theoretical problem. Want a practical answer? Children of up to 10 people will significantly increase the likelihood of passing on their genes to further generations of descendants.

04.08.2009, 09:47

Gee. IMHO genes do not have TTL and a dominant gene can theoretically exist forever... :)

07.08.2009, 15:07

Practical question: in what case is a man more likely to pass on his genes to further generations of descendants - if he has one boy or two girls?

School problem. What does "the probability of passing on one's genes" mean? Three possible clarifications:

1) Maximize the number of descendants carrying the same alleles (let’s assume for simplicity that they are unique; in reality this is not the case, because children will marry in the same population, and the same genes rotate there, but let’s put this aside for clarity). It is clear that in the case of two girls the advantage is twofold.

2) Maximize the number of different alleles passed on to descendants. In the case of two girls, the probability of transmitting two different alleles of a heterozygous gene is 1/2, in the case of one boy - 0.

3) The probability of transmitting the Y chromosome to all further male generations. In the case of a girl, it is obviously 0, if there is a boy, then 1. But at the same time, for any parental couple, for each copy of the Y chromosome gene (or mtdna) passed on to the next generation, there are 4 copies of any gene from a non-sex chromosome and 3 copies of a gene from X chromosomes. Therefore, the probability of preserving the Y chromosome in all further generations is 4 times lower than that for autosomal genes.

07.08.2009, 15:43

After how many generations at most will there be nothing left of his specific genes with a probability of 80-90%?

The problem is very artificial and it can be solved theoretically only if we make the assumption that all the alleles of this lost ancestor are somehow “marked” and were not found in anyone else on earth, and this person had only one line of descendants ending with you - otherwise his You will get genes from many ancestral lines. Next, you need to decide at what number of points each chromosome will recombine during meiotic transmission, that is, during the transfer of genes with recombination. The number of such points (recombination hotspots) is not constant, as it has now turned out. Since during one meiosis some recombination points are used and during another - others, then for a rough estimate their number will have to be taken in excess. We can assume that from some ancestor in such and such a generation (between the 20th and 30th, say) on a certain specific chromosome with such and such a probability (quite large) you do not have a single gene left, and then raise this probability to 23 degree.

Descendants receive from each parent one gene encoding a trait.”

Gregor Mendel is rightly considered the founder of modern genetics, and the pea he experimented with is as famous in scientific folklore as Newton's apple. His scientific research in the monastery orchard in the city of Brünn (now Brno in the Czech Republic), initially motivated only by an interest in agriculture, grew into a many-year series of labor-intensive experiments in plant crossing, as a result of which Mendel came to the conclusion that heredity is determined by genes.

His work was simple, but painstaking: he put special bags on pea flowers so that each plant was pollinated only with carefully selected pollen. Then, by comparing the characteristics of parent and daughter plants, he was able to deduce the laws of inheritance.

Mendel's classic experiments involved crossing two lines of peas - a tall one and a short one. All daughter plants of the first generation were tall (and not at all short or medium height, as expected). However, when the plants of the first generation were subsequently crossed with each other, only three quarters of the daughter plants of the second generation turned out to be tall, the remaining plants were short. To explain the results of these (and many other) experiments, Mendel postulated the following:

- there is a unit of heredity (Mendel called it a “factor”; we now call it a gene), and the daughter organism receives from each parent one gene encoding a given trait;

- if a daughter organism receives genes responsible for alternative traits, then one of these genes will be dominant and will be expressed (that is, the trait encoded by this gene will appear in the organism), and the other will be recessive (that is, not expressed).

In the case of peas, this means that each first-generation daughter plant received both a “tall” gene and a “short” gene—one from each parent. The high growth of the first generation offspring indicates the dominance of the “tall stature” gene. However, in the hereditary material of each daughter plant of the first generation, the unexpressed “short stature” gene was also preserved. In the next generation, one plant will have on average two “tall” genes, two plants will have one “tall” gene and one “short” gene, and one plant will have two “short” genes; it will be undersized. Using this scheme as a guide, Mendel was able to explain many features of inheritance that had previously remained a mystery: for example, why some diseases (such as hemophilia) are passed on through generations or why brown-eyed parents can have blue-eyed children.

As often happens in the history of science, Mendel's work, completed in 1865, did not immediately receive due recognition from his contemporaries. The results of his experiments were published at a meeting of the Society of Natural Sciences of the city of Brünn, and then published in the journal of this Society, but Mendel’s ideas did not find support at that time. Although this journal was received by more than a hundred scientific organizations around the world, the issue of the journal describing Mendel's revolutionary work collected dust in libraries for thirty years. Only at the end of the 19th century did scientists working on the problems of heredity discover the works of Mendel, and he was able to receive (posthumously) the recognition he deserved.

This does not mean that Mendel's ideas were accepted unconditionally. The scientific world has long discussed the theory of preformationism, according to which the egg and sperm somehow contain a miniature adult organism. For example, Anton van Leeuwenhoek (1632-1723), the scientist who introduced the microscope into scientific use, believed that each sperm already contained a tiny human organism, and the egg was needed only to provide it with the nutrients necessary for growth. The question was what controls the development of the embryo - internal, hereditary factors, as Mendel believed, or external environmental factors that could, for example, influence the nutrients of the egg. Today, when scientists can trace in detail the path of development of an organism from a fertilized egg, it turns out that external factors, for example, substances that have an intrauterine effect on the embryo, can cause the “switching on” of certain genes and thus influence the development of the organism.

Today we know that genes discovered by Mendel are sections of DNA molecules found in a cell. According to the central dogma of molecular biology, the mechanism of action of genes is to encode proteins, which, in turn, acting as enzymes, regulate all chemical reactions in living organisms.

Found in the "Popularization of Science" group: vk.com/reason_science

The popular computer game Assassin's Creed, which was recently made into a movie, is based on the idea that the main character is able to "remember" and relive the memories of his long-dead ancestors. In the game and film, a special machine - the Animus - helps the heroes remember the distant past and go through generations.

Although such excursions into the past are now nothing more than science fiction, the idea of ​​genetic memories embedded in our DNA is not so far from the truth.

Transferring the experience of ancestors

In fact, a stunning new study published in the journal Science suggests that experiences that shaped the lives of ancestors can have an impact on the lives of descendants. This connection can remain in the genes for 14 generations.

A team of scientists from the Barcelona Center for Genomic Regulation and the José Carreras Leukemia Research Institute conducted a study on the genes of nematode worms. They concluded that genes are capable of carrying information that potentially reflects the life experiences of distant ancestors.

This discovery captured a unique phenomenon - the longest-lasting form of transmission of genetic information ever discovered in an animal.

What does it mean?

It is still extremely difficult to make similar observations with people, since the life expectancy of people is much longer and the genetic structure is more complex, but the differences in the organization of the genetic material of people and nematode worms are not too radical.

We know that the way our grandparents lived their lives does influence our behavior, but now it's possible that an ancestor who lived centuries ago can still directly influence the way we behave today.

Genetics and genetic memory

Let's digress a little into what exactly genetics does and how we get our DNA from our parents. This is a very specific and relatively new area of ​​biology.

Our genes are inherited from our parents, and their genes are inherited from their parents. If they change or mutate, we inherit those mutations.

However, changes in the genome depend not only on what has been inherited, but also on the environment and life experiences. For example, a lifetime in a hot climate will prepare our bodies to better cope with high temperatures and bright sun, and we can pass this information on to our descendants through changes in the genome.

Changes in the environment and life experiences, such as air and water pollution, war, stress and psychological disorders, greatly influence the information carried by genes.

An additional layer of information received from the experience of parents is, as it were, superimposed on top of the DNA chain. Her structure as such does not change, but her “clothing” changes.

Similar transmission of genetic information, derived from the environment and life experiences of ancestors, has already been seen in humans. For example, descendants of Holocaust survivors have significantly reduced levels of cortisol (the stress hormone) in their blood, which means that they are more susceptible to the negative effects of stress, pressure, tension, anxiety and fear.

Conducted research

This particular study focused on Caenorhabditis elegans - tiny nematodes with a very short lifespan. The researchers genetically engineered them by adding a fluorescent protein to their genes, whose behavior they could monitor under ultraviolet light.

The scientists first placed the worms in a cold environment where the gene glowed faintly. By moving the nematodes to a warmer environment, the scientists saw that the gene glowed much more strongly. After returning the study animals to the cold room, observers noticed that the gene continued to glow more intensely, as if retaining a “memory” of the warm environment.

Subsequently, not only the fluorescent gene, but also the memory of the warm habitat were passed on to subsequent generations. This means that the descendants of the first nematodes with a fluorescent gene “knew” about a warm environment, without ever experiencing it themselves.

conclusions

Scientists suggest that this form of long-term transmission of genetic experience to descendants is a unique form of biological planning for the future. Worms are very short-lived, so it is likely that ancestors pass on memories of the conditions they experienced to help their descendants prepare for what their environment might be like in the future.

So, if worms can “remember” the experiences of their long-gone ancestors, is the same possible for humans? At the moment it is impossible to get a definite answer to this question, but the possibility exists.