Heredity ensures continuityGenerations, the transfer of traits from parents to children. However, the descendants of living organisms are not complete copies of their parents, since hereditary information is capable of changing.
Heredity and variability are one of the most important properties of the living.
Variability is the ability of living organismsTo acquire new properties that distinguish them from other individuals. Even identical twins are at least something, but they are different. Variability of organisms can be modification and hereditary, i.e. Phenotypic and genotypic.
All signs of the body are determined by the genotype. At the same time, the degree of manifestation of a particular genetic characteristic depends on the conditions of the external environment and can be completely different. It is important to understand that inheritance is not transmitted by the sign itself, but only by the ability to exercise it under certain conditions.
Modification changes in characteristics do not affect genes and are not passed on to the next generation. Most often such changes are subject to quantitative characteristics - weight, height, fertility and others.
Different signs may depend on the surroundingEnvironment to a greater or lesser extent. Thus, the color of the eyes and blood group in humans are determined exclusively by genes, and the conditions of life can not affect them in any way. But growth, weight, muscle mass, physical endurance strongly depend on external conditions - physical activity, quality of nutrition, etc.
On the other hand, no matter how much you train and do not eatOatmeal porridge, build muscle mass and develop endurance can only be up to the set limits. These limits, within which any feature is capable of changing, are called the norm of reaction. It is genetically determined and inherited.
Hereditary variability is the basis of diversityLiving organisms, the "supplier" of material for natural selection and the main cause of evolution. It affects genes. Genetic variability has two forms - combinative and mutational.
Combinative variability is based on sexualProcess, recombination of genes during the formation of gametes and the random character of gamete encounter during fertilization. These processes operate independently of each other and create a huge variety of genotypes.
The cause of mutational variability is the appearance ofChanges in DNA molecules. Mutations that occur under the influence of external and internal factors can affect both individual chromosomes and their groups.
Mutagenic factors significantly increase the number ofMutations in the DNA. These include ionizing and ultraviolet radiation (the latter is especially dangerous for light-skinned people), elevated temperature, mercury and lead salts, chloroform, formalin, dyes from the class of acridins. Viruses can also cause mutations.