Final answer:
P and N nucleotide additions refer to the addition of nucleotides during gene recombination processes, resulting in increased diversity of antibodies.
Step-by-step explanation:
Nucleotide additions refer to the process of adding nucleotides to a DNA or RNA molecule during replication or synthesis. There are two types of nucleotide additions known as P and N nucleotide additions.
P nucleotide additions occur during the recombination of immunoglobulin genes in B cells. These additions involve the addition of nucleotides at the junction of gene segments, which increases the diversity of antibodies.
N nucleotide additions, on the other hand, occur during the joining of DNA ends in the process of V(D)J recombination. They involve the addition of random nucleotides at the junction, which also contributes to antibody diversity.