Which of the following explains when a recessive gene is passed on?
when a genetic mutation occurs
when the trait is in its second generation
when the father exhibits the recessiv
when both parents possess the recessive allele

D) "when both parents possess the recessive allele"

Explanation:

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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.