The types of variability.
The causes of modification
variability.
learning Objectives
•classify the types of variability
•explain the causes of modification
variability
Success criteria
1.Know about types of variation.
2.Explain the types of variation: modification variability, mutation
variability, variability of discontinuous and continuous.
3.Carry out research on reasons of emergence of modification
variability.
4.Describe research methods indicating the number of
measurements they plan to take, e.g. how many people they select
and what range should be selected.
5.Describe research process. Explain reasons of emergence of
modification variability.
6.Draw conclusions.
Variability is the ability of living organisms to acquire new marks.
Variability
Phenotypic
(non hereditary)
Modification
Genotypic
(hereditary)
Mutation
Combination
 https://www.youtube.com/watch?v=jUHokSPkzT8
 https://www.youtube.com/watch?v=VjlE5Qzl1S0
 https://www.youtube.com/watch?v=_LoPYfhTgeI
Variation
• Results from genetic and environmental factors
• In biology, any difference between cells, individual
organisms, or groups of organisms of any species caused
either by genetic differences (genotypic variation) or by the
effect of environmental factors on the expression of the
genetic potentials (phenotypic variation).
• Variation may be shown in physical appearance,
metabolism, fertility, mode of reproduction, behavior,
learning and mental ability, and other obvious or
measurable characters.
Genotypic variations
• Genotypic variations are caused by differences in number or
structure of chromosomes or by differences in the genes
carried by the chromosomes.
• Gene mutation: point, deletion, substitution
• Change in chromosomes structure: deletion, translocation,
inversion, duplication.
• Abnormal chromosomes numbers: aneuploidy, polyploidy
• Genetic recombination: free assortment, crossing over,
random fusion
Genetic Variation Causes
•Genetic variation occurs mainly through
DNA mutation, gene flow (movement of
genes from one population to another) and
sexual reproduction. Due to the fact that
environments are unstable, populations that
are genetically variable will be able to adapt
to changing situations better than those
that do not contain genetic variation.
Environmentally factors
• Environmentally caused variations may result from one
factor or the combined effects of several factors, such as
climate, food supply, and actions of other organisms.
• Phenotypic variations also include stages in an organism’s
life cycle and seasonal variations in an individual. These
variations do not involve any hereditary alteration and in
general are not transmitted to future generations;
• consequently, they are not significant in the process of
evolution.
Classification of variation
• continuous, or quantitative
• discontinuous, or qualitative
Continuous variation
Discontinuous variation
The genetic basis of discontinuous variation
In discontinuous (qualitative) variation:
• different alleles at a single gene locus have large
effects on the phenotype
• different genes have quite different effects on
the phenotype.
continuous variation
The genetic basis of continuous variation
In continuous (quantitative) variation:
• different alleles at a single gene locus have small effects on
the phenotype
• different genes have the same, often additive, effect on the
phenotype
• a large number of genes may have a combined effect on a
particular phenotypic trait; these genes are known as
polygenes.
discontinuous variation
Environmental effects on the phenotype
phenotype = genotype + influences of the
environment
The causes of modification
variability
Modification variability
Ice
Natural environment
High temperature
Length of leaves
Dandelion leaves
valley
Highlands of the Alps
variation curve of pumpkin seeds along
the length
Norm of
reaction
purity of
sign
Low rate
high rate
Length of seeds/ mm