Gene, genome, chromosome: definition, structure, functions

"Gene", "gene", "chromosome" – words that are familiar to every schoolboy. But the idea of this question is quite generalized, so as to deepen in the biochemical jungle requires special knowledge and a desire to understand it all. And it is, if present at the level of curiosity, then quickly disappears under the weight of presentation. Let's try to understand the intricacies of genetic information in scientific polar form.

What is a gene?

Gene – the smallest structural and functional piece of information about heredity in living organisms. In fact it is a small piece of DNA, which contains the knowledge about the sequence of amino acids to build protein or functional RNA (which will also be the synthesized protein). The gene determines the characteristics that are inherited and passed on to descendants further down the genealogical chain. Some unicellular organisms there are gene transfer, which has nothing to do with the reproduction of their own kind, it is called horizontal.

"On the shoulders" of genes responsible for how it will look and work each cell and the organism as a whole. They rule our life from the moment of conception to the last breath.

The First scientific step forward in the study of heredity was made by the Austrian monk Gregor Mendel, who in 1866 published his observations on the results in the crossing of peas. The hereditary material, which he used clearly showed the patterns of transmission of characteristics, such as color and shape of peas and flowers. This monk formulated the laws that shaped the beginning of genetics as science. Inheritance of genes occurs because parents give their children half of all their chromosomes. Thus, the signs mom and dad's mix to form a new combination of existing features. Fortunately, more options than living beings on the planet, and it is impossible to find two absolutely identical beings.

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Mendel showed that nakedest­governmental inclinations do not mix and are passed from parents to offspring in the form of discrete (separate­governmental) units. These units represented individuals in pairs (alleles) remain discrete and are passed via the­the next generation in male and female ha­met, each of which contains one unit­CE of each pair. In 1909, Danish botanist Johansen named these units genes. In 1912, a geneticist from the United States of America Morgan showed that they are in chromosomes.

Since then, it took more than a half century, and studies have advanced further than Mendel had imagined. At the moment, scientists have focused on the opinion that the information in genes determines the growth, development and function of living organisms. And maybe even their death.

Classification

The gene Structure contains not only information about the protein, but indicate when and how to read and empty lots required to separate the information about different proteins and stop the synthesis of informational molecules.

There are two forms of genes:

1. Structural – they contain information about the structure of proteins or RNA chains. The nucleotide sequence corresponds to the arrangement of amino acids.
2. Functional genes responsible for the correct layout of all the other DNA parts, for the timing and sequence of its reading.

Today, scientists can answer the question: how many genes in the chromosome? The answer will surprise you: about three billion pairs. And this is just one of twenty-three. The genome is called the smallest structural unit, but it can change a person's life.

Mutations

The Accidental or deliberate change in nucleotide sequence within the DNA is called a mutation. She can hardly affect the structure of the protein, and can completely distort its properties. So there will be a local or global consequences of such changes.

By Themselves, mutations can be pathogenic, that is, to manifest as disease or lethal, not allowing the body to develop to being viable. But most change is imperceptible to humans. Deletions and duplications occur constantly in DNA, but do not affect the course of life of each individual.

Deletion – the loss of a segment of a chromosome that contains certain information. Sometimes such changes are beneficial to the body. They help him to defend against external aggression, such as human immunodeficiency virus and bacteria of the plague.

Duplication-doubling of a segment of a chromosome, and hence the set of genes that it contains, also doubles. Due to the repetition of information makes it worse is subject to selection, and therefore can quickly accumulate mutations and change the body.

Properties of the gene

Every man there is a huge DNA molecule. Genes are functional units in its structure. But even these small areas have their own unique properties, allowing to maintain stability of organic life:

1. A Resolution – the ability of genes to be mixed.
2. Stability – the preservation of the structure and properties.
3. Lability – the abilityto change under the influence of circumstances, to adapt to hostile conditions.
4. Multiple allelism – the existence within the DNA of the genes, encoding the same protein, have a different structure.
5. Allalmost – the presence of two forms of the same gene.
6. Specificity-one sign = one gene is inherited.
7. Pleiotropy – the multiplicity of effects of a single gene.
8. Expression – the severity of the symptom, which is encoded data of the genome.
9. Penetrance – frequency of occurrence of a gene in the genotype.
10. Amplification – the appearance of a large number of copies of a gene in DNA.

Genome

Human Genome – the entire hereditary material in a single human cell. It provides guidance on the construction of the body, organs, physiological changes. The second definition of this term reflects the structure of concepts, not function. The human genome is the totality of genetic material, packaged in a haploid set of chromosomes (23 pairs) and belonging to a specific type.

The Basis of the genome is a molecule of deoxyribonucleic acid, well known as DNA. All genomes contain at least two types of information: coded information about the structure of molecules-mediators (called RNA), and protein (this information is contained in genes), and instructions that define the time and place of the manifestation of this information in the development of the body. The genes themselves occupy a small portion of the genome, but are its Foundation. The information recorded in the genes — a kind of instruction for making proteins the main building blocks of our body.

However, for complete characterization of the genome not sufficiently embedded in the information about the structure of proteins. Need more data about the elements of the genetic apparatus which take part in the work of genes, regulate their expression at different stages of development and in different situations.

But even this is not enough for a complete determination of the genome. Because it contains elements that contribute to its self-reproduction (replication), compact packaging of DNA in the nucleus and even some strange, yet the areas sometimes referred to as “selfish” (that is, if employees only for themselves). For all these reasons, at the moment when it comes to the genome, usually referring to the totality of the DNA sequences presented in the chromosomes of cell nuclei of certain kinds of organisms, including, of course, genes.

Size and structure of the genome

It is Logical to assume that the gene, genome, chromosome vary among representatives of life on Earth. They can be infinitely small, and huge and contain billions of pairs of genes. Gene structure will also depend on whose genome you are researching.

The ratio between the size of the genome and the number of constituent genes can distinguish two classes:

1. Compact genomes with no more than ten million bases. They have a set of genes strictly correlated with size. The most characteristic of viruses and prokaryotes.
2. Large genomes composed of more than 100 million base pairs, with no relationship between their length and number of genes. More common in eukaryotes. Most of the nucleotide sequences in this class do not code for proteins or RNA.

Studies have shown that the human genome is about 28 thousand genes. They are unevenly distributed across the chromosomes, but the value of this feature remains a mystery to scientists.

Chromosomes

Chromosomes – this method of packaging genetic material. They are in the nucleus of each eukaryotic cell, and consists of one very long DNA molecule. They can easily be seen in the light microscope in the fission process. A karyotype is the complete set of chromosomes which is specific for each species. Mandatory elements for them are the centromeres, telomeres and replication.

Changes of the chromosomes during cell division

Gene, genome, chromosome – consistent chains of transmission of information, where each one includes the previous one. But they undergo certain changes during the life of the cell. For example, in the interphase (between divisions) the chromosomes in the core are loose, take up much space.

When a cell prepares for mitosis (i.e., the process of splitting in two), the chromatin is compacted and twisted into chromosomes, and now it becomes visible in the light microscope. In metaphase the chromosomes resemble sticks close to each other and connecting the primary constriction, or centromere. It is responsible for the spindle formation, when the groups of chromosomes line up. Depending on the placement of the centromere there is a classification of chromosomes:

1. Acrocentric – in this case, the centromere is located diametrically relative to the center of the chromosome.
2. Submetacentric when the shoulders (i.e. the areas located before and after the centromere) of unequal length.
3. Metacentric if the centromere divides the chromosome exactly in the middle.

This classification of chromosomes was proposed in 1912 and used by biologists until the present day.

Abnormalities of chromosomes

As with other morphological elements of a living organism with chromosomes can also occur structural changes that affect their functions:

1. Aneuploidy. This change in the total number of chromosomes in the karyotype by adding or removing one of them. The consequences of such mutations can be lethal for the unborn fetus and lead to birth defects.
2. Polyploidy. Is reflected in the increase in the number of chromosomes, a multiple of half their number. Most often found in plants, such as algae and fungi.
3. Chromosomal aberrations, or adjustment is the change in the structure of chromosomes under the influence of environmental factors.

Genetics

Genetics is the science that studies the patterns of heredity and variability, and enable their biological mechanisms. Unlike many other biological Sciences, it from its inception, aspired to be an exact science. The whole history of genetics — a history of the creation and use of increasingly accurate methods and approaches. The ideas and methods genetics play an important role in medicine, agriculture, genetic engineering, industrial Microbiology.

Heredity - the ability of an organism to provide in a number of generations the continuity of morphological, biochemical and physiological characteristics and features. In the process of succession to reproduce the main species-specific group (ethnic, population) and family friendly features of the structure and functioning of organisms and their ontogeny (individual development). Inherited not only the specific structural and functional characteristics of the body (facial features, and some features of metabolic processes, temperament, etc.), but also physico-chemical features of the structure and functioning of the main biopolymers of the cell. Variability-the diversity of characteristics among members of a particular species, but also the property of the descendants to acquire the differences from parent forms. Variability along with heredity are two inseparable properties of living organisms.

Down Syndrome

Down's Syndrome-a genetic disease in which the karyotype has 47 chromosomes instead of normal 46. This is one of the forms of aneuploidy, as discussed above. In the twenty-first pair of chromosomes appears plus, which adds extra genetic information in the human genome.

The name of the syndrome was in honor of the doctor, Donna downs, who discovered and described it in literature as a form of mental disorder in 1866. But the genetic background was discovered almost a hundred years later.

Epidemiology

At the moment the karyotype 47 chromosomes in humans occurs once per thousand births (earlier statistics was different). This was possible due to early diagnosis of this pathology. The disease does not depend on the race, ethnicity of the mother or her social position. Influenced by age. The chances of having a baby with down syndrome increase after thirty-five years, and after forty, the ratio of healthy children to sick already equals 20 to 1. The age of the father over forty years also increases the chances of having a child with aneuploidy.

Forms of down syndrome

The Most common type – the appearance of an extra chromosome in the twenty-first pair of a non-hereditary way. It is because during meiosis the pair are not at odds on the spindle. Five percent of cases is observed mosaicism (extra chromosome is not present in all cells of the body). Together, they comprise ninety-five percent of the total number of people with this congenital pathology. The remaining five percent of cases of hereditary syndrome caused by trisomy of the twenty-first chromosome. However, the birth of two children with this disease in one family is negligible.

Clinic

Man with down syndrome is characterized by external signs, here are some of them:

- flat face;
- cropped skull (lateral size larger longitudinal);
- skin fold on the neck;
- the skin fold that covers the inner corner of the eye;
- excessive mobility of joints;
- reduced muscle tone;
- flattening of the occiput;
- short legs and toes;
- the development of cataracts in children older than eight years old;
developmental abnormalities of the teeth and the hard palate.
congenital heart defects;
- it is possible to have epileptic syndrome;
is the leukemia.

But clearly the diagnosis based only on the external manifestations, of course, impossible. It is necessary to conduct karyotyping.

Conclusion

Gene, genome, chromosome - it seems that it's just words, the meaning of which we understand very generally and vaguely. But in fact, they strongly influence our lives, and changing, forced to change us. The person is able to adapt to the circumstances, whatever they may be, and even for people with genetic anomalies is always a time and place where they will be irreplaceable.