If you do not have an SSN and are not eligible to obtain an SSN, but you have a requirement to furnish a federal tax identification number or file a federal income tax return, you must apply for an ITIN. By law, an alien individual cannot have both an ITIN and an SSN.
DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix.
Every nucleotide in the coding strand has a complementary nucleotide in the other strand, called the template strand. The Watson-Crick pairs are the standard DNA and RNA base pairs. In DNA, adenine bonds to thymine while guanine bonds with cytosine. The same pairs apply to RNA, except that uracil replaces thymine.