Variations may he caused either by the effect of environment or by the changes in the genetic material.There are two main types of variations in genetics, continuous variations and discontinuous variations.Mutation, gene flow and sexual reproduction are three sources of variation.
Now we learn in detail about variation with its types, sources and examples.
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- ENVIRONMENTAL VARIATIONS
- Environmental variations are caused by the
effect of the environment and they cannot be
inherited to the offspring. Such variations have
no significance in the process of evolution.
- Development of muscles in athletes
- The boring of pinna or nose for pulling on
jewellery.
- Loss of some body part due to accident or
disease.
- HERITABLE VARIATIONS
- Heritable variations are caused by changes in
genetic material. They arc considered as raw material for evolution.
GROUPS OF VARIATION
- Depending upon the effects they produce, variations he divided into two groups.
- CONTINUOUS VARIATIONS
- Continuous variations refer to small differences in characters of the members of a species.
- They appear to be the combination of both environmental and genetical factors.
- Height, skin colour, intelligence, eye colour etc. Such variations arc neither
nor purely environmental.
- DISCONTINUOUS VARIATIONS .
- These variations are sudden and sharp differences among
the members of the same species. They aria heritable as they
purely caused by the genetic material.
Examples
- Blood group, six fingers in hand or foot, tongue rolling etc.
CAUSES OF VARIATIONS
Following are the important causes of variations
- INDEPENDENT ASSORTMENT OF CHROMOSOMES
- During mctapha.se of first meiotic division homologous chromosomes come together in thc
form of pairs and subsequently segregate into the daughter cells in dependent of each other.
this produces a wide variety of different gametes.
CROSSING OVER
- Crossing over the mutual exchange of equal segments of chromatids of non sister
Chromatids of a pair cl homologous chromosomes during prophase- I of first meiotic
division. Through crossing over, indefinite combinations of different alleles are made
possible.
FERTILIZATION
- The set of alleles carried by chromosomes of each gamete is unique and always differs to a
more or less extent than the others.
- Since a number of male gametes are available to fertilize female gamete.
- Thus different combinations of characters in individuals are possible as a result of
fertilization of egg with either of male gamete.
MUTATION
- Mutation can be defined as a sudden change in the genetic material. It is the most important
source of heritable variation among the organisms which is considered as the starting point
of new species.
- It has been a common observation that some individuals of a population show strikingly
different characters than the others. For example six fingers in hands or feet.
ENVIRONMENT
- A number of environmental factors affect the body cells to cause variations. For instance,
The change in pigmentation of skin upon the extent of exposure to sunlight or the
development of muscles due to exceres etc.
- Such variations arc non he itahlc.
