For many centuries science has led to very important discoveries that would help treat various diseases or explain a particular fact in nature and its origin. Modern gene theory has been able to take a huge step in the treatment of rare diseases. She also gave explanations on thousands of issues related to the origin and hereditary factors of humanity and its development.
A bit of history
A few decades ago, the gene carried an abstract concept. Scientists found that he was responsible for the transfer of heredity from parents to children, but they could not fully understand the exact mechanism.
With the development of biochemistry as a science, the situation has changed somewhat. It was found that proteins and enzymes are involved in the processes. Thus, research into the modern theory of the gene started. Then, with the development of molecular biology as a science, the situation completely changed and took steps to uncover the secrets of heredity forward.
It was revealed that the gene is not an abstract concept, but a material substance. Now it has become clear that this is a certain sequence of DNA sections that are converted into messenger RNA and participate in the formation of protein.
Deoxyribonucleic acid
Each cell has a molecule that is responsible for heredity and is responsible for all genetic information. That is, hair color, putative growth, and other signs are encoded in DNA.
This molecule takes the form of a double helix. The chains in DNA are complementary, if you have one of them, then using the rule, it is easy to implement the other. This molecule consists of 4 components - adenine (A), thymine (T), guanine (G) and cytosine (C). In a chain they have a certain sequence. Thymine always follows adenine, and cytosine follows guanine. Such pairs are called nucleotides.
How do these chains encode the whole organism? According to the decoding of the human genome, it consists of 3 billion pairs of nucleotides. And that’s just half the chromosomes. This amount contains complete information about the human body. Interestingly, in primates, most of the genome coincides with the human.
How is the transfer of heredity?
DNA is transcribed first. This process is called transcription. During it, the chains are woven with the help of many chemical reactions. The result is a complementary m-RNA (ribonucleic acid). This molecule is very similar to DNA, but instead of thymine, it produces uracil (Y).
For example, DNA had the sequence AGTGTSTAGHTST, then m-RNA after transcription will look like UTSAGAUTSGSA. That is, the DNA sequence rule will work.
Cells of complex organisms have in their structure a nucleus containing all the DNA. Then the m-RNA chain is cleaved from deoxyribonucleic acid, with which it was transcribed and leaves the nucleus, leaving for ribosomes. There, proteins are translated from m-RNA. In this process, several more types of molecules take part. First of all, this is transport ribonucleic acid (t-RNA). They act as carriers of amino acids from which proteins are formed.
In this process, m-RNA acts as a template for the t-RNA molecule. For example, insulin has 150 nucleotide pairs and is 50 amino acids. Together it forms a gene. All proteins are encoded by this type of molecule.
What is a gene?
This concept has changed its interpretation for a long time. Finally, it has been established and sounds like this: a gene - consists of many DNA molecules that occupy a certain area, it is responsible for the manifestation and development of a certain trait.
According to modern gene theory, the human body is made up of 50 trillion cells. All of them have different shapes and carry their own functions. Inside each of them is a core containing almost 99.9% of the genes. The rest are located in the mitochondria. There are about 20,000 genes in total.
DNA is a double-stranded molecule consisting of sugar, phosphate and four nucleotides (adenine, thymine, cytosine, guanine). They form the genetic code. The number and order of nucleotides determines whether the creature is a monkey, a cow, a banana, or a person.
Most genes are “recipes” for making proteins. And they are transmitted from parents to children, from generation to generation. For example, if it is said that the child has paternal hair, then this means the baby inherited from dad genes that encode proteins that tell the particles of hair follicles to grow curly or even hair, like their ancestors.
Gene functions
Genes control the functioning of cells and give signs. In particular, they can turn their other representatives on and off to control the functions of different organelles. A large DNA molecule containing genes is broken down into several parts called chromosomes. Their number in different species is not repeated.
In humans, according to the current state of gene theory, there are 46 of them - two sets of 23 pieces (pairs). And, for example, chimpanzee chromosomes have 24 pairs, cows have 30, and bananas have 11. The interesting question is, how many percent of DNA matches other people?
In 99.5%, a similarity occurs. What then sets us apart? The answer is quite simple - single nucleotide polymorphisms.
Gene concept
With the development of science, genetics began to move forward by leaps and bounds. Several rules have been established regarding the concept of a gene.
- It cannot be divided into subunits by breaking chromosomes or rearranging them, which means it is an extreme unit of structure.
- It is considered the main one over the definition of one function in metabolism, and it cannot be divided into subfunctions, which means the gene is an extreme unit of function.
So there was a hypothesis - "one gene - one enzyme." Over time, this rule has somewhat transformed into "one gene - one m-RNA and one polypeptide."
What is SNP?
The current state of gene theory claims that the main package of 23 pairs of chromosomes in all people is called their genome. It has 3 million base pairs. In the process of rearranging them during crossing, a replacement occurs, and a difference is formed in one of them. It is called a single nucleotide polymorphism (SNP).
During the formation of new cells, certain errors may occur. It happens that when reproducing the genome to form a new cell, the body skips, adds or replaces one base pair.
The permutation of the base pair is called the SNP. When decoding the human genome, about 10 million structures are obtained that are responsible for many external and internal differences between all people on the planet. Some SNPs regulate growth, eye color, physique, etc., while others encourage the development of various diseases.
Genotypes of men and women
Children receive such sections of DNA from mom and dad, and those, in turn, from their parents, etc. In humans, there are two sets of chromosomes. Each of them has 23. One of them the child receives from one of the parents.
On any chromosome that has passed from mother, the same from the pope is inherited, variants of the same genes are encrypted in it. Such a pair is called homologous chromosomes.
But X and Y are special species. Typically, women have two X, and men XY chromosomes. In any case, the child receives one option from the mother - X, and one of the two can pass from the father. If X gets from the father, then XX is formed in the pair - a girl is born, and if Y gets, then the combination XY is formed - a boy is born.
The bulk of adult cells contains two sets of chromosomes. The sperm and egg each carry one set. In the process of their formation, the cells go through the division phase, and the pairs diverge. According to one of the chromosomes, from a pair in a chaotic order they fall into each new cell. This means that 50% of the genes are inherited from the mother, and 50% from the father.
But other children from the same pair will not necessarily receive the same gene combinations that the first descendant received. Another option arises only with the birth of identical twins.
During the formation of a sperm or egg, the process of doubling the chromosomes begins, and they can intersect. This happens at random points, and DNA exchange begins. This process is called recombination.
In this case, the genes are "shuffled", so the chromosomes that pass to the descendants are not similar to those that were received from their parents. But Y chromosomes always go along the male line unchanged. What mitochondrial DNA is inherited by the child only through the female line, so heredity is best checked using the Y chromosome or mitochondrial DNA.
When the sperm and egg combine during fertilization, one cell is formed with two full sets of 23 chromosomes - one from a woman and the other from a man. This cell divides in the future a huge number of times, forming new ones, until the fetus is fully formed.
Phenotype and its features
Distinctive characteristics, called the phenotype, are formed as a result of the interaction of genes and the environment. Such a process begins in the womb of the mother and then continues throughout life.
The difference in some phenotypes, such as growth, is determined to a large extent by genes. If parents and immediate ancestors did not differ high, then the child is unlikely to be higher than all peers. But sometimes, this process can be slightly affected by nutrition.
The effect of genes on personality is less studied. Character traits are developed to a greater extent throughout life than genetically laid.
Introduction to Heredity
Modern gene theory provides an opportunity to understand how the transmission of one or another trait from parents to children occurs. To understand this process, you need to understand what recessive and dominant genes are.
Mendel gave about these theses in his theory. Dominant is a gene that prevails over a recessive one. In genetics, it is denoted by any capital Latin letter.
Now let's look at an example. Suppose the mother has brown eyes, the dominant gene is responsible for them (denoted by B), and the father has blue eyes and the recessive one is responsible for this sign (note b). In this case, during fertilization, only brown eyes can form in the fetus on this basis, since the dominant from the mother will always prevail in the allele (crossing variation).
If both parents have a combination of Bb, in which the capital letter is brown eyes, and the small letter is blue, then the following combinations can turn out:
- BB - brown eyes;
- Bb - hazel;
- Bb - hazel;
- bb - blue.
These estimates indicate that in 75% the child will have brown eyes. And only in 25% of the offspring blue can form. As you can see, the recessive gene was received by both parents from their ancestors, and they became its carriers. That is why the blue-eyed babies are sometimes born to the brown-eyed father and mother.
Modern Gene Theory: Key Points
After several decades of research, there are constant concepts that define genetics:
- nucleic acids serve as a material substrate for the transmission of hereditary factors;
- genes are responsible for the main processes and reactions associated with enzymes;
- one gene may be responsible for several traits;
- a certain number of genes can be responsible for one trait and the more there are, the brighter the manifestations;
- a gene contains data on only one protein;
- genes can mutate.
These points describe modern gene theory. The main properties of the gene characterize a DNA site containing information about heredity.