Disadvantage of asexual reproduction are

The major disadvantage of asexual reproduction is that all descendants of the same parent are genetically equal (population is uniform). If the environmental conditions of the place change and are no longer conducive to these individuals, they may disappear. In a population with genetic variability, however, some beings can survive in the new environmental conditions and thus maintain themselves.

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.