heredity and variation in nature because there are chromosomes, genes, deoxyribonucleic acid (DNA).Stored and transferred genetic information in the form of a chain of nucleotides in DNA.What role in this phenomenon belongs to the genes?What is a chromosome from the perspective of the transmission of hereditary traits?Answers to such questions will understand the principles of coding and genetic diversity on our planet.Largely dependent on how much is included in a set of chromosomes from the recombination of these structures.
From the history of the discovery of "particles of heredity»
examined under a microscope the cells of plants and animals, many botanists and zoologists still in the middle of the XIX century, drew attention to the finest threads and tiny ring-shaped structure in the nucleus.Most other chromosomes called a pioneer of the German anatomist Walther Flemming.That he used aniline dyes for the processing of nuclear structures.Fleming discovered a substance called "chromatin" for his ability to staining.The term "chromosome" in 1888 ushered in the scientific revolution Heinrich Valdeyer.
Along with Flemming was looking for an answer to the question of what a chromosome, the Belgian Edouard Van Beneden.Earlier German biologist Theodor Boveri and Eduard Strasburger conducted a series of experiments to prove the individuality of chromosomes, the constancy of the number of different species of living organisms.
Background chromosomal theory of heredity
American researcher Walter Sutton learned how chromosomes contained in the cell nucleus.The scientist believed these structures carrier units of heredity characteristics of the organism.Sutton found that chromosomes consist of genes, through which are passed from parents to offspring properties and functions.Genetics in the publications described the chromosome pairs, their movement in the division of the cell nucleus.
Regardless of the American colleagues working in the same direction led Theodor Boveri.Both researchers in the works studied the transfer of hereditary characteristics, formulated the basic provisions on the role of chromosomes (1902-1903).Further development of the theory of Boveri-Sutton took place in the laboratory of Nobel laureate Thomas Morgan.A prominent American biologist and his aides have established a number of laws governing the distribution of genes in the chromosome, developed cytological base that explains the mechanism of the laws of Gregor Mendel - the founding father of genetics.
chromosomes in the cell
study of the structure of chromosomes began after their discovery and description in the XIX century.These corpuscles and filaments found in prokaryotic organisms (non-nuclear) and eukaryotic cells (nuclei).A study under the microscope revealed that a chromosome with a morphological point of view.It is moving filamentary body that discernible in certain phases of the cell cycle.The entire volume of the interphase nucleus chromatin takes.In other periods distinguishable chromosome in one or two chromatids.
best seen these formations during cell division - mitosis or meiosis.In eukaryotic cells often may be observed large linear chromosome structure.In prokaryotes, they are smaller, although there are exceptions.Cells often include more than one type of chromosomes, such as their own small "particles of heredity" is in the mitochondria and chloroplasts.
forms chromosomes
Each chromosome has an individual structure, different from the other features of the staining.In the study of morphology it is important to determine the position of the centromere, the length and location of the shoulders relative to the waist.The set of chromosomes is usually composed of the following forms:
- metacentric or-equal, which is characterized by the location of the median centromere;
- submetacentric or neravnoplechie (hauling biased towards one of the telomeres);
- acrocentric, or rod-shaped, in which the centromere is located almost at the end of chromosomes;
- of point to difficult to define the shape.
functions chromosomes
chromosome consists of genes - functional units of heredity.Telomeres - the ends of the chromosome arms.These specialized elements serve to protect from damage, prevent sticking fragments.Centromere carries out its tasks with a doubling of the chromosomes.It has a kinetochore is attached to it spindle structure.Each pair of chromosomes individual at the location of the centromere.Filaments spindle operated so that the daughter cells extends along one chromosome, and not both.Uniform doubling in the fission process provides the origin of replication.Duplication of each chromosome begins simultaneously in several of these points, which significantly speeds up the whole process of division.
role of DNA and RNA
find out what a chromosome, which is the function of the nuclear structure failed after studying its biochemical composition and properties.In eukaryotic cells, nuclear chromosomes are formed by fused material - chromatin.According to the analysis, it is composed of high molecular weight organic substances:
- deoxyribonucleic acid (DNA);
- ribonucleic acid (RNA);
- histone protein.
Nucleic acids are taking a direct part in the biosynthesis of amino acids and proteins that provide transmission of hereditary characteristics from generation to generation.DNA contained in the nucleus of a eukaryotic cell, the RNA is concentrated in the cytoplasm.
Genes
X-ray analysis showed that the DNA forms a double helix, which consists of a chain of nucleotides.They represent a carbohydrate deoxyribose, a phosphate group and one of four nitrogenous bases:
- A - adenine.
- G - guanine.
- T - thymine.
- C - cytosine.
Land dezoksiribonukleoproteidnyh helical filaments - it genes carrying coded information about the sequence of amino acids in proteins or RNA.During the multiplication of hereditary characteristics from parents to offspring transmitted as alleles.They determine the functioning, growth and development of a particular organism.According to some researchers, those sections of DNA that do not encode polypeptides perform regulatory functions.The human genome may have up to 30 thousand. Genes.
set of chromosomes
total number of chromosomes, their features - a characteristic feature of the species.In the fly Drosophila their number - 8, in primates - 48, the person - 46. This number is a constant for the cell organisms that belong to the same species.For all eukaryotes there is a concept "diploid chromosomes."This full set, or 2n, unlike haploid - half the number (n).
chromosomes within a single pair of homologous identical in form, structure, location centromere, and other elements.Homologues have their own characteristics that distinguish them from other chromosomes in the set.Staining basic dyes allows us to consider, explore the distinctive features of each pair.Diploid set of chromosomes present in somatic cells, haploid same - in the genital (the so-called gametes).In mammals and other organisms with male sex heterogametic formed two types of sex chromosomes: X chromosome and Y. Males have a set of XY, females - XX.
human chromosome set
human cells contain 46 chromosomes.All of them are combined in 23 pairs that make up the set.There are two types of chromosomes autosomes and sex.The first form 22 pairs - are common to women and men.They are characterized by a pair of 23th - sex chromosomes, which are the cells of the male body are non-homologous.
genetic traits associated with sex.For transmission are Y and X chromosome from males two X women.Autosomes contain the rest of the information about hereditary characteristics.There are techniques to individualize all 23 pairs.They are clearly distinguishable in the drawings, when painted in a certain color.It is noticeable that 22-chromosome in the human genome - the smallest.Its DNA has a stretched length of 1.5 cm and a population of 48 million base pairs.Specific proteins from the histone chromatin perform compression, whereupon the thread take thousands of times less space in the cell nucleus.Under the electron microscope, the histones in the interphase nucleus resemble beads strung on a strand of DNA.
Genetic diseases
There are more than 3 thousand. Different types of hereditary diseases caused by injuries and abnormalities in chromosomes.These include Down syndrome.For a child with a genetic disease characterized by the lag in mental and physical development.In cystic fibrosis there is a failure in the functions of exocrine glands.Report leads to problems with sweating, separation and accumulation of mucus in the body.It is difficult for the lungs, can lead to suffocation and death.
Violation of color vision - blindness - immunity to some parts of the color spectrum.Hemophilia weakens clotting.Lactose intolerance does not allow the human body to digest milk sugar.In the offices of family planning can be found on the predisposition to a particular genetic disease.In large medical centers have the opportunity to receive appropriate assessment and treatment.
Gene therapy - the direction of modern medicine, the elucidation of the genetic causes of hereditary diseases and its elimination.With the latest techniques in pathological cells instead of the broken normal genes are introduced.In this case, the doctors did not relieve the patient from symptoms, and on the causes of the disease.Correction is performed only somatic cell gene therapy is not applied in large quantities in relation to the gametes.
