Dna is comprised of four different types of nucleotides. each one is made up of a pentose sugar, a phosphate group, and one of four nucleosides. 2. adenine, guanine, cytosine and thymine are nitrogenous bases. 3. adenine and guanine, which have a nine-member double-ring, are called purines. 4. cytosine and thymine, which have a six-member single-ring, are called pyrimidines.

Answers to mastering biology drag the labels to their appropriate locations to complete the punnett squares for morgan's reciprocal cross. drag blue labels onto the blue targets to indicate the genotypes of the parents and offspring. drag pink labels onto the pink targets to indicate the genetic makeup of the gametes (sperm and egg). labels can be used once, more than once, or not at all. hints