How does a gene mutation happen?

A gene mutation can occur because of environmental factors. If a person is exposed to UV lights it can cause a mutation to happen

Gene mutations happen when the DNA has a frameshift cause the DNA to be mutated this can be transferred genetically.

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The person who utilize the progression principle will keep adding the difficulty of the exercise that he's doing, while the person who does not, will only stay stagnant.  the person that utilize progression principle, will get a stronger endurance because now his body is conditioned to do harsher routines.{the answer was already on verified)