If one is attempting to determine the influence of genes or the environment on phenotypic variation, inbred strains with individuals of a relatively homogeneous or constant genetic background are often used. variation observed between different inbred strains reared in a constant or homogeneous environment would likely be caused by genetic factors, while variation observed among members of the same inbred strain reared under varying environmental conditions would likely be caused by what source?

Variation observed between different inbred strains reared in a constant or homogeneous environment are often times caused by genetic factors, while variation observed among members of the same inbred strain reared under varying environmental conditions would likely be caused by nongenetic factors.

These Non-genetic factors transfers the parental phenotype or environmental components that causes variation in gene expression during offspring development.

Examples of the non genetic factors are the constituents that make up the ancestral environment which plays a role in variation among the offspring.

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explanation:

organisms that lack symmetry are called asymmetrical and belong to phylum porifera/sponges.

organisms with specialized stinging cells belong to phylum cnidaria. stinging cells are called cnidoblast cells.

cnidarians show two morphological forms : polyp (sessile) and medusa (mobile)

filter feeding is observed in porifera members.  

alternation of generation is observed in coelenterata or cnidaria. there is alternation of asexual polyp form and sexual medusoid form. it is also referred as metagenesis.