Chromosome theory of heredity

Hopes and fears about who will belike a future child, from which parents inherit the intellect and what character traits he will inherit always accompany moms, dads, grandmothers and grandfathers throughout pregnancy and during infancy. But not so much depends on the parents themselves - there is a chromosome theory of heredity, genetics and ... the case.

It is known that human chromosomes containinggenes, are divided into two types - autosomes and sex chromosomes. Some genetic features are associated with human sex, while autosomes contain the remainder of hereditary information. A gene is a segment of DNA containing a number of nucleotides, the sequence of which is genetic information, which subsequently leads to the formation of specific features of the organism. They are of two types - dominant and recessive. The method of recording genetic information in genes, consisting of a nucleotide sequence, is called a genetic code.

Both eggs and sperm at the moment of conception bringtheir 23 pairs needed to determine the genetic code of the fetus. Even then, the color of the future child's eyes, his physical structure, distinctive tendencies and inclinations are laid. This magic number of 23 means that both the mother and the father transmit only half of their genetic capital - something that can not be predicted. That is, each characteristic of the child is the result of crossing the material of both parents. 22 autosomes are numbered by size. The other two chromosomes, X and Y, are sex chromosomes. This picture of human chromosomes is arranged in pairs and is called a karyotype.

Heredity, which plays in the processreproduction is an important role, is a fundamental property of living organisms and their characteristics - morphological, physiological, biochemical or psychological. The basic laws of heredity were formulated in 1866 by G. Mendel, who is considered the founder of the science of genetics. He stated that individual properties, which depend on specific hereditary factors (later called genes), when forming gametes are divided and participate in their fertilization. As a result, people with different combinations of paternal and maternal genes are born.

The work of Mendel was continued by the American geneticistThomas H. Morgan. His chromosome theory of heredity is based on the results of studies of flies -busters. He came to the conclusion that genes located in different chromosomes are inherited independently of each other. The fusion of chromosomes during fertilization is of great importance in the transfer of hereditary properties. Each pair contains similar genes, and the simplest forms of inheritance can be associated with one pair of genes.

In addition, the chromosome theory of heredityand also about possible violations of the adhesion of genes. Failures in the normal number of chromosomes in cells and are the main cause of human genetic diseases. Some chromosomal abnormalities do not cause disease in the carrier, although with a high probability they can lead to the birth of a child with an abnormal amount of chromosomes (chromosomal syndrome). This pathology can be expressed in a reduced number of chromosomes, the presence of their copies, the reverse direction or attachment of a part of the chromosome to another chromosome. Most mutations are fairly neutral and have no effect on human development. Exceptions are chromosomal aberrations that alter the structure of chromosomes.

Morgan's research was not in vain. His chromosome theory of heredity has been confirmed and, what is especially important, further development in the study of the nature of the gene.