Heredity
and variation
Genetics is often
described as a science which deals with heredity and variation.
Heredity: Heredity is the
transmission of characters from parents to offsprings.
Variation: The organisms belonging
to the same natural population or species that shows a difference in the
characteristics is called variation. Variation is of two types (i) Discontinuous
variation and (ii) Continuous variation
Within a population
there are some characteristics which show a limited form of variation. Example:
Style length in Primula, plant height of garden pea. In discontinuous
variation, the characteristics are controlled by one or two major genes which
may have two or more allelic forms. These variations are genetically determined
by inheritance factors. Individuals produced by this variation show differences
without any intermediate form between them and there is no overlapping between
the two phenotypes. The phenotypic expression is unaffected by environmental
conditions. This is also called as qualitative inheritance.
This variation may be
due to the combining effects of environmental and genetic factors. In a
population most of the characteristics exhibit a complete gradation, from one
extreme to the other without any break. Inheritance of phenotype is determined
by the combined effects of many genes, (polygenes) and environmental factors.
This is also known as quantitative inheritance. Example: Human height and skin
color.
·
Variations make some individuals better fitted in the struggle
for existence.
·
They help the individuals to adapt themselves to the changing environment.
·
It provides the genetic material for natural selection
·
Variations allow breeders to improve better yield, quicker growth,
increased resistance and lesser input.
·
They constitute the raw materials for evolution.
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