Many mutations can occur in the human body, changing its gene structure, and, consequently, its characteristics. This also applies to proteins responsible for the formation of blood groups. There are 2 of them in total - agglutinogens A and B, located on the membrane of erythrocytes. Inherited from parents, these antigens create a combination that determines one of four groups blood.

You can calculate the possible blood groups of a child based on the blood groups of the parents.

In some cases, a child is found to have a completely different blood type than the one that could have been inherited from the parents. This phenomenon was called the Bombay Phenomenon. It occurs as a result of a rare genetic mutation in one in 10 million people (Caucasians).

This phenomenon was first described in India in 1952: the father had blood type 1, the mother had blood type 2, and the child had blood type 3, which is normally impossible. The doctor who studied this case suggested that in fact the father did not have the first blood type, but its imitation, which arose as a result of some genetic changes.

Why does this happen?

The basis for the development of the Bombay phenomenon is recessive epistasis. In order for an agglutinogen, for example, A, to appear on an erythrocyte, the action of another gene is necessary, it was called H. Under the influence of this gene, a special protein is formed, which is then transformed into a genetically programmed agglutinogen. For example, agglutinogen A is formed and determines the 2nd blood group in humans.

Like any other human gene, H is present on each of the two paired chromosomes. It encodes the synthesis of an agglutinogen precursor protein. Under the influence of a mutation, this gene changes in such a way that it can no longer activate the synthesis of the precursor protein. If it happens that two mutated hh genes enter the body, then there will be no basis for the creation of agglutinogen precursors, and there will be neither protein A nor B on the surface of red blood cells, since they will have nothing to form from. When examined, such blood corresponds to I (0), since it does not contain agglutinogens.

With the Bombay phenomenon, the child's blood type does not follow the rules of inheritance from the parents. For example, if normally a woman and a man with group 3 can give birth to a child also with group 3 III (B), then if they both pass on recessive h genes to the child, the precursor of agglutinogen B will not be able to form.

How to recognize the Bombay phenomenon?

Unlike the first blood group, when it does not have agglutinogens A and B on red blood cells, but there are agglutinins A and B in the blood serum, in individuals with the Bombay phenomenon, agglutinins are determined by the inherited blood group. In the example discussed above, although there will be no agglutinogen B on the child’s red blood cells (reminiscent of blood group 1), only agglutinin A will circulate in the serum. This will distinguish blood with the Bombay phenomenon from normal blood, because normally individuals with group 1 have both agglutinins - a and b.

There is another theory that explains possible mechanism Bombay phenomenon: when germ cells form, a double set of chromosomes remains in one of them, while in the second there are no genes responsible, among other things, for the formation of blood groups. However, embryos formed from such gametes are most often nonviable and die on early stages development.

Patients with this phenomenon can only be transfused with exactly the same blood. Therefore, many of them keep their own material at blood transfusion stations so that they can use it if necessary.

When getting married, it is better to warn your partner in advance and consult a geneticist. Patients with the Bombay phenomenon most often give birth to children with a normal blood type, but one that does not comply with the rules of inheritance from the parents.

How does it work (from the point of view of cell biochemistry)…

On the surface of our red blood cells there are carbohydrates - “H antigens”, also known as “0 antigens”.(On the surface of red blood cells there are glycoproteins that have antigenic properties. They are called agglutinogens.)

Gene A encodes an enzyme that converts some H antigens into A antigens.(Gene A encodes a specific glycosyltransferase that adds the residueN-acetyl-D-galactosamineto an agglutinogen, resulting in agglutinogen A).

Gene B encodes an enzyme that converts some H antigens into B antigens. (Gene B encodes a specific glycosyltransferase that adds the residue D-galactose to agglutinogen, resulting in agglutinogen B).

Gene 0 does not code for any enzyme.

Inheritance of blood groups. Bombay phenomenon...

For example, let's cross parents with groups 1 and 4 and see why they havethere cannot be a child with 1

(Because a child with type 1 (00) should receive a 0 from each parent, but a parent with blood type 4 (AB) does not have a 0.)

Inheritance of blood groups. Bombay phenomenon...

Bombay phenomenon

It occurs when a person does not produce the “original” antigen H on his red blood cells. In this case, the person will have neither antigens A nor antigens B, even if the necessary enzymes are present.

Example: a person with the AA genotype must have blood group 2. But if he is AAHh, then his blood type will be the first, because there is nothing to make antigen A from.

This mutation was first discovered in Bombay, hence the name. In India, it occurs in one person in 10,000, in Taiwan - in one in 8,000. In Europe, hh is very rare - in one person in two hundred thousand (0.0005%).

Inheritance of blood groups. Bombay phenomenon...

An example of the Bombay phenomenon at work:if one parent has the first blood group, and the other has the second, then the child can't have fourth group, because none of them

parents do not have the B gene required for group 4.

Polymerism…

Polymerism is the interaction of non-allelic multiple genes that unidirectionally influence the development of the same trait; The degree of manifestation of a trait depends on the number of genes. Polymer genes are designated by the same letters, and alleles of the same locus have the same subscript.

Polymer interaction of non-allelic genes can be

cumulative and non-cumulative.

With cumulative (accumulative) polymerization, the degree of manifestation of the trait depends on the total action of several genes. The more dominant gene alleles, the more pronounced a particular trait is. Segregation in F2 according to the phenotype during dihybrid crossing occurs in the ratio 1: 4: 6: 4: 1, and in general corresponds to the third, fifth (with dihybrid crossing), seventh (with trihybrid crossing), etc. lines in Pascal's triangle.

Polymerism…

With non-cumulative polymerization, the signmanifests itself in the presence of at least one of the dominant alleles of polymer genes. The number of dominant alleles does not affect the degree of expression of the trait. Segregation in F2 according to phenotype during dihybrid crossing is 15:1.

Polymer Example- inheritance of skin color in humans, which depends (to a first approximation) on four genes with a cumulative effect.

From school we know that there are four main blood types. The first three are common, but the fourth is rare. The groups are classified according to the content of agglutinogens in the blood, which form antibodies. However, few people know that there is also a fifth group, called “ bombay phenomenon».

To understand what we're talking about, you should remember the content of antigens in the blood. So, the second group contains antigen A, the third contains antigen B, the fourth contains antigens A and B, and the first group does not contain these elements, but it contains antigen H - this is a substance that takes part in the construction of other antigens. In the fifth group there is neither A, nor B, nor H.

Inheritance

Blood type determines heredity. If parents have the third and second groups, then their children can be born with any of the four groups, if the parents have the first group, then the children will only have blood of the first group. However, there are cases when parents give birth to children with an unusual, fifth group or Bombay phenomenon. This blood does not contain antigens A and B, which is why it is often confused with the first group. But in Bombay blood there is no antigen H, contained in the first group. If a child turns out to have the Bombay phenomenon, then it will not be possible to accurately determine paternity, since there is not a single antigen in the blood that his parents have.

History of discovery

The discovery of an unusual blood type was made in 1952, in India, in the Bombay region. During malaria, massive blood tests were carried out. During the examinations, several people were identified whose blood did not belong to any of the four known groups, since it did not contain antigens. These cases were called the "Bombay phenomenon". Later, information about such blood began to appear all over the world, and in the world, for every 250,000 people, one has a fifth type. In India, this figure is higher - one per 7,600 people.

According to scientists, the emergence new group in India is due to the fact that consanguineous marriages are allowed in this country. According to Indian laws, procreation within a caste allows one to preserve one’s position in society and family wealth.

What's next

After the discovery of the Bombay phenomenon, scientists at the University of Vermont made a statement that there are other rare blood types. The latest discoveries are named Langereis and Junior. These species contain completely unknown proteins responsible for blood type.

The uniqueness of the 5th group

The most common and oldest is the first group. It arose during the time of the Neanderthals - it is more than 40 thousand years old. Almost half of the world's population has the first blood group.

The second group appeared about 15 thousand years ago. It is also not considered rare, but according to various sources, about 35% of people are carriers of it. Most often, the second group is found in Japan and Western Europe.

The third group is less common. Its carriers are about 15% of the population. Most people with this group are found in Eastern Europe.

Until recently, the fourth group was considered the newest group. About five thousand years have passed since its appearance. It occurs in 5% of the world's population.

The Bombay phenomenon (blood group V) is considered the newest, as it was discovered several decades ago. There are only 0.001% of people on the entire planet with such a group.

Formation of the phenomenon

The classification of blood groups is based on the content of antigens. This information applies to blood transfusions. It is believed that the H antigen contained in the first group is the “progenitor” of all existing groups, since it is a kind of building material from which antigens A and B appeared.

Pawning chemical composition blood changes occur in utero and depend on the blood groups of the parents. And here geneticists can tell which possible groups a baby may be born with by carrying out simple calculations. Sometimes deviations from the usual norm do occur, and then children are born who exhibit recessive epistasis (Bombay phenomenon). Their blood does not contain antigens A, B, H. This is the uniqueness of the fifth blood group.

People with the fifth group

These people live the same way as millions of others, with other groups. Although there are some difficulties for them:

1. It's difficult to find a donor. If a blood transfusion is necessary, only the fifth group can be used. However, Bombay blood can be used for all groups without exception, and there are no consequences.
2. Paternity cannot be established. If you need to do a DNA paternity test, it will not give any results, since the child will not have the antigens that his parents have.

There is a family in the USA in which two children were born with the Bombay phenomenon, and even with A-H type. Such blood was detected once in the Czech Republic in 1961. There are no donors for children in the world, and transfusions from other groups are fatal for them. Because of this feature, the eldest child became his own donor, and the same thing awaits his sister.

Biochemistry

It is generally accepted that there are three types of genes responsible for blood groups: A, B and 0. Each person has two genes - one gets from the mother, and the second from the father. Based on this, there are six gene variations that determine blood type:

1. The first group is characterized by the presence of 00 genes.
2. For the second group - AA and A0.
3. The third contains antigens 0B and BB.
4. In the fourth - AB.

Carbohydrates are located on the surface of red blood cells, they are also antigens 0 or antigens H. Under the influence of certain enzymes, antigen H is encoded into A. The same thing happens when antigen H is encoded into B. Gene 0 does not produce any encoding of the enzyme. When there is no synthesis of agglutinogens on the surface of erythrocytes, i.e., there is no original H antigen on the surface, then this blood is considered Bombay. Its peculiarity is that in the absence of the H antigen, or “source code,” there is nothing to convert into other antigens. In other cases, various antigens are found on the surface of red blood cells: the first group is characterized by the absence of antigens, but the presence of H, the second - A, the third - B, the fourth - AB. People with the fifth group do not have any genes on the surface of their red blood cells, and they don’t even have H, which is responsible for coding, even if there are enzymes that are encoded - it is impossible to convert H into another gene, because this source H does not exist.

The original H antigen is encoded by a gene called H. It looks like this: H is the gene that encodes the H antigen, h is a recessive gene in which the H antigen is not formed. As a result, when carrying out genetic analysis possible inheritance of blood groups in parents, children may be born with different group. For example, parents with the fourth group cannot have children with the first group, but if one of the parents has the Bombay phenomenon, then they can have children with any group, even with the first.

Conclusion

Over many millions of years, evolution has been taking place, and not only of our planet. All living beings change. Evolution has not abandoned blood either. This liquid not only allows us to live, but also protects us from negative impact environment, viruses and infections, neutralizing them and preventing them from penetrating vital systems and organs. Similar discoveries made by scientists decades ago in the form of the Bombay phenomenon, as well as other types of blood groups, remain a mystery. And it is unknown how many secrets that have not yet been revealed by scientists are kept in the blood of people around the world. Maybe after some time it will become known about another phenomenal discovery of a new group, which will be very new, unique, and the people with it will have incredible abilities.

There are three types of genes responsible for blood group - A, B, and 0 (three alleles).

Every person has two blood type genes - one received from the mother (A, B, or 0), and one received from the father (A, B, or 0).

There are 6 possible combinations:

How it works (from the point of view of cell biochemistry)

On the surface of our red blood cells there are carbohydrates - “H antigens”, also known as “0 antigens”.(On the surface of red blood cells there are glycoproteins that have antigenic properties. They are called agglutinogens.)

Gene A encodes an enzyme that converts some H antigens into A antigens.(Gene A encodes a specific glycosyltransferase that adds an N-acetyl-D-galactosamine residue to an agglutinogen to produce agglutinogen A).

The B gene encodes an enzyme that converts some H antigens into B antigens.(Gene B encodes a specific glycosyltransferase, which adds a D-galactose residue to an agglutinogen, resulting in agglutinogen B).

Gene 0 does not code for any enzyme.

Depending on the genotype, carbohydrate vegetation on the surface of red blood cells will look like this:

For example, let’s cross parents with groups 1 and 4 and see why they have a child with group 1.

(Because a child with type 1 (00) should receive a 0 from each parent, but a parent with blood type 4 (AB) does not have a 0.)

Bombay phenomenon

It occurs when a person does not produce the “original” antigen H on his red blood cells. In this case, the person will have neither antigens A nor antigens B, even if the necessary enzymes are present. Well, great and powerful enzymes will come to convert H into A... oops! but there’s nothing to transform, there’s no one!

The original H antigen is encoded by a gene, which is unsurprisingly designated H.
H - gene encoding antigen H
h - recessive gene, H antigen is not formed

Example: a person with the AA genotype must have blood group 2. But if he is AAHh, then his blood type will be the first, because there is nothing to make antigen A from.

This mutation was first discovered in Bombay, hence the name. In India, it occurs in one person in 10,000, in Taiwan - in one in 8,000. In Europe, hh is very rare - in one person in two hundred thousand (0.0005%).

An example of the Bombay phenomenon No. 1: if one parent has the first blood group, and the other has the second, then the child has the fourth group, because neither of the parents has the B gene necessary for group 4.

And now the Bombay phenomenon:

The trick is that the first parent, despite its BB genes, does not have B antigens, because there is nothing to make them from. Therefore, despite the genetic third group, from the point of view of blood transfusion, he has the first group.

An example of the Bombay phenomenon No. 2. If both parents have group 4, then they cannot have a child of group 1.

And now the Bombay phenomenon

As we see, with the Bombay phenomenon, parents with group 4 can still get a child with group 1.

Cis position A and B

In a person with blood type 4, during crossing over, an error (chromosomal mutation) may occur when both genes A and B appear on one chromosome, but nothing on the other chromosome. Accordingly, the gametes of such an AB will turn out strange: one will contain AB, and the other will have nothing.

Of course, chromosomes containing AB and chromosomes containing nothing at all will be rejected by natural selection, because they will have difficulty conjugating with normal, non-mutant chromosomes. In addition, AAV and ABB children may experience a gene imbalance (impaired viability, death of the embryo). The probability of encountering a cis-AB mutation is estimated at approximately 0.001% (0.012% cis-AB relative to all AB).

Example of cis-AV. If one parent has group 4, and the other has group 1, then they cannot have children of either group 1 or 4.

And now the mutation:

The probability of having children shaded in gray is, of course, less - 0.001%, as agreed, and the remaining 99.999% falls on groups 2 and 3. But still, these fractions of a percent “should be taken into account during genetic counseling and forensic medical examination.”

The human body is famous for its uniqueness. Due to various mutations that occur daily in our body, we become individual, since some of the characteristics that we acquire differ significantly from the same external and internal factors of other people. This also applies to blood type.

It is usually customary to divide it into 4 types. However, it is extremely rare, but it happens that a person who should have one (due to genetic characteristics parents) has a completely different, specific. This paradox is called the “Bombay phenomenon”.

What it is?

This term refers to a hereditary mutation. It is extremely rare - up to 1 case per ten million people. The Bombay phenomenon gets its name from the Indian city of Bombay.

In India, there is one settlement where people have a “chimeric” blood type quite often. This means that when determining erythrocyte antigens using standard methods, the result shows, for example, the second group, although in fact, due to a mutation in a person, the first.

This occurs due to the formation of a recessive pair of genes H in a person. Normally, if a person is heterozygous for this gene, then the trait does not appear, the recessive allele cannot perform its function. Due to the incorrect combination of parental chromosomes, a recessive pair of genes is formed, and the Bombay phenomenon occurs.

How does it develop?

History of the phenomenon

A similar phenomenon was described in many medical publications, but almost until the middle of the 20th century, no one had any idea why this was happening.

This paradox was discovered in India in 1952. The doctor, conducting a study, noticed that the parents had the same blood groups (the father had the first, and the mother the second), and the born child had the third.

Having become interested in this phenomenon, the doctor was able to determine that the father’s body had managed to somehow change, which made it possible to believe that he had the first group. The modification itself occurred due to the absence of an enzyme that allows the synthesis of the required protein, which would help determine the required antigen. However, since there was no enzyme, the group could not be determined correctly.

The phenomenon is quite rare among representatives. It is somewhat more common to find carriers of “Bombay blood” in India.

Theories of the origin of Bombay blood

One of the main theories for the emergence of a unique blood type is chromosomal mutation. For example, in a person with it is possible to recombine alleles on chromosomes. That is, during the formation of gametes, the genes responsible for can move as follows: genes A and B will end up in one gamete (the subsequent individual can receive any group except the first), and the other gamete will not carry the genes responsible for the blood type. In this case, inheritance of a gamete without antigens is possible.

The only obstacle to its spread is that many such gametes die without even entering embryogenesis. However, perhaps some survive, which subsequently contributes to the formation of Bombay blood.

It is also possible that gene distribution is disrupted at the zygote or embryonic stage (as a result of maternal malnutrition or excessive alcohol consumption).

The mechanism of development of this condition

As has been said, everything depends on genes.

A person’s genotype (the totality of all his genes) directly depends on the parent, or more precisely, on what characteristics were passed on from parents to children.

If you study the composition of antigens more deeply, you will notice that the blood type is inherited from both parents. For example, if one of them has the first, and the other has the second, then the child will have only one of these groups. If the Bombay phenomenon develops, everything happens a little differently:

• The second blood group is controlled by the gene a, which is responsible for the synthesis of a special antigen - A. The first, or zero, has no specific genes.
• The synthesis of antigen A is due to the action of the section of chromosome H responsible for differentiation.
• If there is a malfunction in the system of this section of DNA, then the antigens cannot differentiate correctly, which is why the child can acquire antigen A from the parent, and the second allele in the genotype pair cannot be determined (conventionally it is called nn). This recessive pair suppresses the action of area A, as a result of which the child has the first group.

If we generalize everything, it turns out that the main process causing the Bombay phenomenon is recessive epistasis.

Non-allelic interaction

As was said, the development of the Bombay phenomenon is based on non-allelic interaction of genes - epistasis. This type of inheritance is distinguished by the fact that one gene suppresses the action of another, even if the suppressed allele is dominant.

The genetic basis for the development of the Bombay phenomenon is epistasis. The peculiarity of this type of inheritance is that the recessive epistatic gene is stronger than the hypostatic gene, but it determines the blood group. Therefore, the inhibitor gene that causes suppression is not capable of producing any trait. Because of this, a child is born with “no” blood type.

This interaction is determined genetically, so it is possible to detect the presence of a recessive allele in one of the parents. It is impossible to influence the development of such a blood group, much less change it. Therefore, for those who have the Bombay phenomenon, the pattern of everyday life dictates some rules, following which, such people will be able to live normally and not fear for their health.

Features of life of people with this mutation

In general, people who carry Bombay blood are no different from ordinary people. However, problems arise when a transfusion is required (major surgery, accident or disease of the blood system). Due to the peculiarity of the antigenic composition of these people, they cannot be transfused with blood other than Bombay. Such errors are especially common in extreme situations when there is no time to thoroughly study the analysis of the patient’s red blood cells.

The test will show, for example, the second group. When a patient is transfused with blood of this group, intravascular hemolysis may develop, which will lead to death. It is precisely because of this incompatibility of antigens that the patient only needs bombay blood, necessarily with the same Rh as his.

Such people are forced to preserve their own blood from the age of 18, so that later they will have something to transfuse if necessary. There are no other features in the body of these people. Thus, we can say that the Bombay phenomenon is a “way of life” and not a disease. You can live with him, you just have to remember your “uniqueness.”

Paternity issues

The Bombay phenomenon is the “thunderstorm of marriage”. The main problem is that when determining paternity, it is impossible to prove the existence of the phenomenon without special research.

If suddenly someone decides to clarify the relationship, then they should definitely be informed that the presence of such a mutation is possible. Genetic match test in such a case should be carried out more extensively, with the study of the antigenic composition of blood and red blood cells. Otherwise, the child’s mother risks being left alone, without a husband.

This phenomenon can only be proven using genetic tests and determining the type of inheritance of blood group. The study is quite expensive and is not currently widely used. Therefore, when a child is born with a different blood type, one should immediately suspect the Bombay phenomenon. The task is not easy, since only a few dozen people know about it.

Bombay blood and its occurrence today

As has been said, people with Bombay blood are rare. This type of blood is practically never found in representatives of the Caucasian race; Among Indians, this blood is more common (on average, among Europeans, the occurrence of this blood is one case per 10 million people). There is a theory that this phenomenon develops due to the national and religious characteristics of the Hindus.

Everyone knows that it is a sacred animal and its meat cannot be eaten. Perhaps because beef contains some antigens that can cause changes, Bombay blood appears more often. Many Europeans eat beef, which serves as a prerequisite for the emergence of the theory of antigenic suppression of a recessive epistatic gene.

Climatic conditions may also have an influence, but this theory is not currently being studied, so there is no evidence to substantiate it.

The significance of Bombay blood

Unfortunately, few people have heard about Bombay blood these days. This phenomenon is known only to hematologists and scientists working in the field genetic engineering. Only they know about the Bombay phenomenon, what it is, how it manifests itself and what needs to be done when it is identified. However, the exact cause of this phenomenon has not yet been identified.

If we look at it from an evolutionary point of view, Bombay blood is an unfavorable factor. Many people sometimes require a transfusion or replacement to survive. In the presence of Bombay blood, the difficulty lies in the impossibility of replacing it with blood of another type. Because of this, deaths often occur in such people.

If we look at the problem from the other side, it is possible that Bombay blood is more advanced than blood with a standard antigenic composition. Its properties have not been fully studied, so it is impossible to say what the Bombay phenomenon is - a curse or a gift.