Now consider a single base mutation in a codon for leucine that creates a codon for phenylalanine. A true reversion changes the phenylalanine codon back to a codon for leucine. Which of the following leucine codon(s) could be mutated once to form a phenylalanine codon, and then mutated at a second site to restore a leucine codon?a. CUU
b. CUC
c. CUA
d. UUG
e. UUA
f. CUG

options A, B, D and E

Explanation:

leucine codons include: UUA, UUG, CUU, CUC, CUA, CUG

phenylalanine codons include: UUU, UUC.

CUU          

replace C with U to give

UUU phenylalanine codon

replace underlined with A

UUA leucine codon

CUC

replace underlined with U

UUC phenylalanine codon

replace underlined with A or G

UUA, UUG  leucine codons

UUG

replace underlined with U

UUU phenylalanine codons

replace underlined with C

CUU leucine codon

UUA

replace underlined with U or C

UUU or UUC phenylalanine codons

replace U with C

CUU or CUC leucine codons

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.