Two genes for the same trait are compared. which one is not an example of a mutation?
in the first, the series is adenine followed by two thymine; in the second, adenine is followed by two thymine.
in the first, the series is cytosine - adenine - thymine; in the second, it is cytosine - adenine - adenine.
the first has thymine where the second has a guanine.
the first has a series of three nucleotide bases; the other has a series of four.

The cytosine-adenine-adenine pair is not an example of mutation.

Explanation:

In the base pairing of DNA, adenine bonds only with thymine and guanine bonds with cytosine. As guanines and adenines are purines and thymine and cytosine are pyrimidine in DNA, and due to their structure, there is only small space in between them to fit a purine and pyrimidine and not more than that.

Therefore, these constructions of two adenines are not possible with cytosine. Thus, this cannot be an example of mutation.

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.

americans began to notice growing differences between the northern and southern sections of the country. there were more people living in cities in the north, which made it more urban. more people lived on farms in the south, which made it more rural. while many people were farmers in the northern states, there were now other ways to make a living, such as working in mechanical cotton gins factories manufacturing cloth, tools and other goods. people in the north supported high tariffs on goods imported from europe because the extra cost encouraged people to “buy american” instead. in the southern states, planters did not like tariffs because they sold most of their production to europe and bought their tools from there as well. southerners believed the protective tariff was something that only northern factory owners keep their profits high. so the southern politicians came up with an idea. they would opt out. they would simply ignore the protective tariff. it was ‘null and void’ in south carolina. the state would not collect the taxes on goods imported into south carolina, no matter what the president said they had to do. this decision led to the nullification crisis.