I think it might be sampling
Reaches the adult stage is the correct answer. When an intervebrate reaches the adult stage it has most likely stopped growing and can finally begin reproduction, passing further down the line his genes and the genes of his ancestors.
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Phenotypic variations in genetically identical organisms that grow in the same controlled environment may be due to mutation.
<h3>Mutation</h3>
This refers to a sudden change to the DNA sequence of living organisms.
When the DNA base sequence of organisms changes, the effect is shown in the morphology of organisms.
For organisms that are genetically identical but grow in different environments, phenotypic variations might exist as a result of environmentally acquired traits during the struggle to adapt to their environments.
In the same environment, however, genetically identical organisms are not expected to be phenotypically different, unless a mutation to the DNA of one has occurred.
More on mutation can be found here: brainly.com/question/17106056