The concept of aging as a result of cellular duplication errors is based on the fact that the body's ability to make new cells that are exact copies of the original ones

Through Mutation

Explanation:

Since our cells are able to produce exact copies of themselves. Thus, until unless some mutation has occurred and affected the ability of the cells to produce exactly similar duplicates copies of the parent cell, there is no way that an individual gets aged.  

Since, mutation affects the mitochondrial DNA it is pretty sure that a mutated cell has affected the longevity of a normal cell and then that mutated cell has produced million other mutated aged cell by replicating itself

Is altered by mutation with time.

Explanation:

The older the age more is the process of aging. The aging includes both physical and psychological. The cellular duplication is a process of cell division called mitosis that produces exact copies of the original ones. The mitochondrial DNA mutation with the age is a cause of ageing. The mutation in somatic cells causes decrease in the function of such cells. The somatic mutations are one of the cause of decreasing the ability of cells to make exact copy of it.

Thus, the concept of aging as a result of cellular duplication errors is based on the fact that the body's ability to make new cells that are exact copies of the original ones is altered by mutation with time.

"do a testcross with a homozygous recessive plant."