Sex chromosomes: The X and Y chromosomes in human beings that detemiine the 

 sex of an individual. Females have two X chromosomes in diploid cells; males have 

 an X and a Y chromosome. The sex chromosomes comprise the 23rd chromosome 

 pair in a karyotype. Compare autosomes. 



Shotgun method: Cloning of DNA fragments randomly generated from a genome. 

 See lihrary. genomic library. 



Shuttle vectors: Cloning vectors that are capable of replicating in both prokaryotic 

 and eukaryotic hosts. 



Single-gene disorder: Hereditary disorder caused by a mutant allele of a single gene 

 (e.g.. Duchenne muscular dystrophy, retinoblastoma, sickle cell disease). Compare 

 polygenic disorders. 



Somatic cells: Any cell in the body except gametes and their precursors. 



Southern blotting: Transfer by absorption of DNA fragments separated in 



electrophoretic gels to membrane filters for detection of specific sequences by 

 radiolabeled complementary probes. 



Spheroplast: Yeast or bacterial cell from which most of the cell wall has been removed 

 by enzymatic or chemical treatment. 



Sticky ends: See cohesive ends. 



Technology transfer: The process of moving scientific findings into the commercial 

 sector for conversion to useful products. 



Telomere: The ends of chromosomes. These specialized structures are involved in the 

 replication and stability of linear DNA molecules. See DNA replication. 



Thymine (T): A nitrogenous base, one member of the base pair, A-T (Adenine- 

 Thymine). 



Transcription: The synthesis of an RNA copy from a sequence of DNA (a gene); the 

 first step in gene expression. Compare translation. 



Transfer RNA. (tRNA): A class of RNA having structures with triplet nucleotide 

 sequences that are complementary to the triplet nucleotide coding sequences of 

 mRN A. The role of tRN As in protein synthesis is to bond with amino acids and 

 transfer them to the ribosomes, where proteins are assembled according to the 

 genetic code carried by mRNA. 



Transformation: A process by which the genetic information carried by an individual 

 cell is altered by incorporation of exogenous DNA into its genome. 



155 



