Recombinant DNA. Illustration of the DNA molecule (Deoxyribonucleic Acid, showing a recombined fragment. DNA carries the inherited instructions of a living organism. Here, a segment of DNA (white, foreground) is joined to, and recombined with, a larger segment of DNA (blue, background). Recombination is used in genetic engineering to incorporate a gene sequence into a DNA strand. The DNA molecule is composed of two strands of atoms twisted into a helical shape. Each strand consists of an outer sugar-phosphate backbone (blue, white) from which nucleotide bases project and link up. The sequence of bases forms the genetic code.