Is there any options to pick from?
Answer:
Thymine
Explanation:
DNA nucleotide bases always attach in specific pairs.
Adenine is always with Thymine and Cytosine is always with Guanine. Here, since one nucleotide is Adenine, we know the other nucleotide is Thymine.
One way to remember this pairing is by this device:
Car in the Garage (cytosine goes with guanine)
and
Apple on the Tree (adenine goes with thymine)
The exoskeleton of an arthropod is chitin.
Non-disjunction occurs when a the chromosomes do not split properly during meiosis resulting in too few chromosomes I believe.