Variability (variation) as a biological phenomenon. Classification of variation. Sources of phenotype variation.

Date: 2015-10-07; view: 425.

THE BASIC THEORETICAL ITEMS OF INFORMATION

Variation is a characteristic of living organisms to change genes and character of ones manifestation.

Sources of phenotype variation are influence of environments factors and changes of genotype.

Classification of variation (variability)

2. Changes of phenotype without change of genes.

3. Changes of phenotype in consequence of genes changes.

Changes of phenotype without change of genes, or modifications of phenotype are a result of environments factors influence only. Herewith genotype does not change. For example trees of one biological species have smaller length in conditions of little rains than in conditions of much rains. This kind of variation doesn't pass from one generation to other generation. The biological signification of this kind of variation is increasing an adaptation degree of organism to changing conditions of external environment within one generation.

As a rule some complex of environmental influences and genes is to form the characteristic of organism. Individually each of these genes has little effect on the phenotype but their combined effect is significant. And some complex of environmental factors act on a variable of phenotype. Thus there is a cumulative effect of environmental factors. But one of them may be the main.

Limits of trait (character) changing are identified as the rate of reaction.

Correlations between the degree of trait expression and frequency of these expression cases are identified as a variational series. Graphic expression of variational series is named as a variational graph.

For instance, the length of mans' body in the population changes from 160 centimeters to 190 centimeters. 160 and 190 centimeters is the limits of expression or the rate of reactions. The determined value of the man' body length and frequency of their cases are distributed in variational series so:

And the determined value of man body length and frequency of their cases are distributed in variational graph.

There are some indexes to give characteristics of variational graph and variational series. The most important among them is middle value (simple average) (M).

M = ∑ (a x b)/ n

∑ - sum , a - body length, b - frequency of cases, n - the sum of cases.

Changes of phenotype in consequence of genes changes are divided to two groups:

a. Formation of new combinations (genotypes) by shuffling of parental genes

b. Modification in chromosomes and genes (DNA) called mutation.