Genetics (from the Greek genetikos - to produce and genesis - birth) is a field of biology; the science of genes, heredity, and variation in organisms. The fact that living beings inherit the traits of their parents has been used since prehistoric times to improve the productivity of crops and animals through selective breeding. However, modern genetics, which seeks to understand the process of inheritance, only really began with the work of Gregor Mendel in the mid-nineteenth century. Although he did not know the physical basis of heredity, Mendel observed that organisms inherit traits through specific discrete units of heredity, which today we call genes.
Genes and chromosomes
Our body is made up of millions of cells. Most cells contain a full set of genes. Humans have thousands of genes. Genes can be compared to instructions that are used to control the growth and coordinated operation of the entire body. Genes are responsible for many traits in our body, such as eye color, blood type, or height.
Genes are located on thread-like structures called chromosomes. Generally, most cells in the body contain 46 chromosomes each. Chromosomes are passed down to us from our parents - 23 from mom, and 23 from dad, so we often look like our parents. Thus, we have two sets of 23 chromosomes, or 23 pairs of chromosomes. Because there are genes on the chromosomes, we inherit two copies of each gene, one copy from each parent. Chromosomes (hence, genes) are made up of a chemical compound called DNA.
Nucleotide sequences in genes are translated by cells to produce a chain of amino acids and to synthesize proteins-the order of amino acids in a protein corresponds to the order of nucleotides in the gene. This relationship between the nucleotide sequence and the amino acid sequence is called genetic code. The amino acids in a protein determine how they make up the three-dimensional form, which, in turn, is responsible for the function of the protein. Proteins perform almost all of the functions necessary for cellular life. Changing the sequence of bases in the part of the DNA molecule that carries the genetic information (gene) can change the sequence of amino acids of a protein, changing its form and function, which often leads to a negative impact on the functioning of cells and the body as a whole. And in most cases there is only a change in of a single nucleotide. Often it is caused by some particular genetic disease, which can be inherited.
Although genetic characteristics play an extremely important role in the appearance, development, functioning and behavior of organisms, the final result (a set of traits and special properties of an organism) is a combination of genetic factors with the conditions in which the development of the organism takes place. For example, heredity plays a significant role in the formation of such a trait as human growth, but nutritional characteristics and other conditions (such as physical activity, specific exercises, etc.) can greatly modulate the said trait depending on the conditions.