Which of the following events could cause a trisomy in a diploid zygote?
A)The cell membrane does not divide at the end of telophase II.
B)Two sister chromatids remain joined during meiosis II.
C)All the answers are correct.
D)The chromosomes do not condense at the beginning of meiosis I.

In a diploid zygote, the cause of trisomy is two sister chromatids remain joined during meiosis II (option B).

Explanation:

At the end of meiosis I, each daughter cell contains a chromosome formed by sister chromatids, each of which must be separated in meiosis II to form the gametes with a chromosome charge equivalent to half the chromosome charge of the species.

The result of the sister chromatids not separating in meiosis II -by not disjunction- results in a gamete with an extra chromosome, which when joined to another gamete results in a zygote with an additional chromosome, which is considered an aneuploidy, called trisomy.

Learn more:

Trisomy link

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.

equal distribution i think.