Base Sequence: Sequential order of bases in a DNA or RNA strand.

adenine: A purine; a nitrogen-containing base in certain nucleotides. Base pairs with thymine in DNA.

bacteriophage Category of viruses that infect bacterial cells.

cloning Making a genetically identical copy of DNA or of an organism.

cytosine: Pyrimidine; one of the nitrogen-containing bases in nucleotides.

deoxyribonucleic acid (DNA): is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms.

DNA ligase: Enzyme that seals new base-pairings during DNA replication.

DNA polymerase: Enzyme of replication and repair that assembles a new strand of DNA on a parent DNA template.

DNA repair: Enzyme-mediated process that fixes small-scale alterations in a DNA strand by restoring the original base sequence.

guanine: Nitrogen-containing base in one of four nucleotide monomers of DNA or RNA.

nucleotide: Small organic compound with deoxyribose (a five-carbon sugar), a nitrogenous base, and a phosphate group.

Thymine: A nitrogen-containing base; one of the nucleotides in DNA.

x-ray diffraction image Pattern that forms on film exposed to x-rays that have been directed at a molecule.

anticodon: Series of three nucleotide bases in tRNA.

base-pair substitution: One amino acid has replaced another during protein synthesis.

carcinogen: Any substance or agent that can trigger cancer.

codon: One of 64 possible base triplets in an mRNA strand.

deletion: loss of a segment from a chromosome. At molecular level, loss of one to a few base pairs from a DNA molecule.

exon: One of the base sequences of an mRNA transcript that will become translated.

Gene mutation: A small-scale change in the nucleotide sequence of a DNA molecule.

genetic code: the basic language of protein synthesis in cells.

insertion: a movable attachment of muscle to bone.

intron A noncoding portion of a pre-mRNA transcript; excised before translation.

Ionizing radiation: High-energy wavelengths.

mRNA (messenger RNA): A single strand of ribonucleotides transcribed from DNA, then translated into a polypeptide chain.

mutation rate: the probability that a spontaneous mutation will occur during or between DNA replication cycles.