What are sources of variation for evolution?
All heritable variations arise due to mutation and only heritable variations are important for evolution.
Some variations are acquired during life time but such variations have no genetic basis.
Variations are common in biological organisms, and such variations arise naturally in population due to mutations. The ultimate source of variation is through genetic mutation.
Natural variations seen in mussels:
Variations that are acquired during life due to environmental influence or habits will not be inherited by progeny.
Variations brought about by mutation changes:
1. either the base sequence of the genetic material,
2. or its location in genome,
3. or its amount.
The first may happen due to an error during DNA replication.
The second happens when chromosomal structures are altered.
The third could be due to aneuploidy or polyploidy.
Mutated genetic material and hence corresponding variation is inherited by the progeny.