Heredity provides continuitygeneration, transmission of traits from parents to children. However, the descendants of living organisms are not complete copies of their parents, as genetic information capable of change.
Heredity and variability - one of the most important properties of living.
Variability - is the ability of living organismsacquire new properties that distinguish them from other individuals. Even identical twins to give us something, but differ from each other. organisms variability can be hereditary and the modification, ie, phenotypic and genotypic.
All signs of the organism are determined by genotype. At the same time, the degree of manifestation of a genetic trait depends on the environmental conditions and may be completely different. It is important to understand that not inherited by the indication itself and its ability to exert only under certain conditions.
Modification changes signs do not affect the genes and are not transmitted to the next generation. Most often such changes are subject to quantitative characteristics - height, weight, fertility and others.
Various features may depend on the ambientenvironment to a greater or lesser extent. For example, eye color and blood group in humans are determined solely by genes, and living conditions affect them in any way can not. But the height, weight, muscle mass, physical endurance are highly dependent on external factors - physical activity, nutrition, etc.
On the other hand, no matter how much you eat or train andoatmeal, build muscle and endurance can only develop up to specified limits. These limits, within which is able to change any indication, called the norm of reaction. It is caused by genetic and inherited.
Hereditary variability - the basis of diversityliving organisms, "supplier" of the material for natural selection and the evolution of the main reason. It affects genes. Genetic variation takes two forms - and combinative mutation.
Combinative variability based on sexualprocess, recombination of genes during the formation of gametes and the random nature of the meeting of gametes at fertilization. These processes operate independently of each other and create a huge variety of genotypes.
Cause of mutation - the emergence ofchanges in DNA molecules. Mutations that occur under the influence of external and internal factors that may affect how individual chromosomes, and their group.
Mutagenic factors greatly increase the number ofmutations in the DNA. These include ionizing and ultraviolet radiation (the latter is especially dangerous for fair-skinned people), elevated temperature, salt, mercury and lead, chloroform, formaldehyde, dyes of the acridine. Is caused by mutations capable and viruses.