Electrophoresis: A method of separating large molecules (such as DNA fragments or 

 proteins) from a mixture of similar molecules. An electric current is passed through 

 a medium containing the mixture, and each kind of molecule travels through the 

 medium at a different rate, depending on its electrical charge and size. Separation is 

 based on these differences. Agarose and acryiamide gels are the media commonly 

 used for electrophoresis of proteins and nucleic acids. 



Endonuclease: An enzyme that cleaves its nucleic acid substrate at internal sites in the 

 nucleotide sequence. 



Enzyme: A protein that acts as a catalyst, speeding the rate at which a biochemical 

 reaction proceeds but not altering the direction or nature of the reaction. 



Eukaryote: Cell or organism with membrane-bound, structurally discrete nucleus and 

 other well-developed subcellular compartments. Eukaryotes include all organisms 

 except viruses, bacteria, and blue-green algae. Compare prokciryote. See 

 chromosome. 



Exons: The protein-coding DNA sequences of a gene. Compare introns. 



Exonuclease: An enzyme that cleaves nucleotides sequentially from free ends of a 

 linear nucleic acid substrate. 



Flow cytometry: Analysis of biological material by detection of the light-absorbing or 

 fluorescing properties of ceils or subcellular fractions (i.e.. chromosomes) passing 

 in a narrow stream through a laser beam. An absorbance or fluorescence profile of 

 the sample is produced. Automated sorting devices, used to fractionate samples, 

 sort successive droplets of the analyzed stream into different fractions depending 

 on the fluorescence emitted by each droplet. 



Flow karyotyping: Use of flow cytometry to analyze and/or separate chromosomes 

 on the basis of their DNA content. 



Gamete: Mature male or female reproductive cell with a haploid set of chromosomes 

 (23 for humans); that is, a sperm or ovum. 



Gene: The fundamental physical and functional unit of heredity. A gene is an ordered 

 sequence of nucleotides located in a particular position on a particular 

 chromosome that encodes a specific functional product (i.e.. a protein or RNA 

 molecule). See gene expression. 



Gene expression: The process by which a gene"s coded infomiation is converted into 

 the structures present and operating in the cell. Expressed genes include those that 

 are transcribed into mRNA and then translated into protein and those that are 

 transcribed into RNA but not translated into protein (e.g., transfer and ribosomal 

 RNAs). 



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