what are the types of variation?
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genetic variations and germinal variations
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Somatogenic
They are somatic and non-inheritable. They are caused by the influence of the environment upon the somatic cells.
For example
Strong sunlight causes skin to darken in humanHoneybee larvae fed on royal jelly become fertile and others that are not become sterile. The fertile larva becomes the queen and the others become workers.Continuous exercise makes the muscles of a sportsmen strong and well developed.Chinese women wear tight shoes in order to get small feet.
In all the above cases, the changes are not heritable and are caused due to changes in the environment.
Blastogenic
There are changes that occur in the genes of the organism. These changes may be heritable. The changes may be due to assortment of genes during meiosis in sexual reproduction or due to some sudden change in the composition of genes or chromosome number. An example of change due to meiosis is the difference in height of a population. An example of change in the number of chromosomes is Down's syndrome where there is an extra 21st chromosome. The individual is mentally retarded, has moon face, thick lips and generally does not live to the reproductive age. An example of change in the gene structure is sickle-celled anaemia. In this, one of the genes undergoes a change in its composition. This results in the red blood cells being sickle shaped. It is a fatal disease.
Variations may also be classified as continuous and discontinuous.
Continuous Variations
Continuous variations are minute and non-hereditary. They may be due to influence of the environment or genetic. For example, variation in height of a human population, number of arms in a starfish, etc.
Discontinuous Variations
Discontinuous variations are large and prominent. They are due to mutations. For example, six digits in man, tailless kitten, hornless calf, etc.
They are somatic and non-inheritable. They are caused by the influence of the environment upon the somatic cells.
For example
Strong sunlight causes skin to darken in humanHoneybee larvae fed on royal jelly become fertile and others that are not become sterile. The fertile larva becomes the queen and the others become workers.Continuous exercise makes the muscles of a sportsmen strong and well developed.Chinese women wear tight shoes in order to get small feet.
In all the above cases, the changes are not heritable and are caused due to changes in the environment.
Blastogenic
There are changes that occur in the genes of the organism. These changes may be heritable. The changes may be due to assortment of genes during meiosis in sexual reproduction or due to some sudden change in the composition of genes or chromosome number. An example of change due to meiosis is the difference in height of a population. An example of change in the number of chromosomes is Down's syndrome where there is an extra 21st chromosome. The individual is mentally retarded, has moon face, thick lips and generally does not live to the reproductive age. An example of change in the gene structure is sickle-celled anaemia. In this, one of the genes undergoes a change in its composition. This results in the red blood cells being sickle shaped. It is a fatal disease.
Variations may also be classified as continuous and discontinuous.
Continuous Variations
Continuous variations are minute and non-hereditary. They may be due to influence of the environment or genetic. For example, variation in height of a human population, number of arms in a starfish, etc.
Discontinuous Variations
Discontinuous variations are large and prominent. They are due to mutations. For example, six digits in man, tailless kitten, hornless calf, etc.
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