variability - the ability of living organisms to acquire new properties that distinguish them from other animals.Even identical twins to give us something, but differ.Variability of organisms and the modification can be hereditary, that is,phenotypic and genotypic.

Modification variability

All signs are determined by the genotype of the organism.At the same time the degree of manifestation of a genetic trait depends on the environmental conditions and can be quite different.It is important to understand that is not inherited by the sign itself, but rather the ability to exercise it in certain circumstances.

signs of modification changes do not affect the genes and are not transmitted to the next ge
neration.In most cases these changes are subject to the quantitative characteristics - height, weight, fertility and others.

Various features may depend on the environment 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 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 any train and eat oatmeal, build muscle and endurance can be developed only to specified limits.These limits within which is able to change any indication, called the norm reaction.It is caused by genetic and inherited.

Hereditary variability

Hereditary variability - the basis of the diversity of living organisms, "supplier" of the material for natural selection and the evolution of the main reason.It affects genes.Genetic variation has two forms - combinative and mutational.

combinative variability based on the sexual process, recombination of genes during the formation of gametes and 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 - changes in the appearance of DNA molecules.Mutations that occur under the influence of external and internal factors may affect how individual chromosomes and their group.

mutagenic factors

mutagenic factors greatly increase the number of mutations 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.Can cause mutations and viruses.