THE HUMAN GENOME AT A GLANCE

URL: http://www.globeandmail.com/gam/Science/20000627/UPRIMN.html 

Date accessed: 15 July 2000 

                     Tuesday, June 27, 2000

                     The human genome is the biological instruction for how an individual is

                     formed and how the cells in the body function.

                     There are more than 50,000 genes -- no one knows exactly how many

                     -- in the human genome.

                     Except for identical twins, the gene structure is unique in each individual.

                     Half the genes in a person come from each parent.

                     Genes direct the formation, or expression, of proteins that a cell uses to

                     function, repair or defend itself, and to divide.

                     Genes are contained in the chromosomes in the nucleus of each cell.

                     There are 22 numbered chromosomes, plus two that determine gender,

                     X and Y. A female has two X chromosomes; a male has an X and a Y.

                     A complete human genome is contained in a coiled double helix of DNA,

                     or deoxyribonucleic acid. Stretched out, the coil would be 1.5-metres

                     long, but only 20 microns wide. A human hair is about 50 microns wide.

                     About three billion DNA subunits, called base pairs, make up the double

                     helix.

                     Base pairs are composed of four types of chemicals, called nucleotides,

                     that are weakly bonded in pairs to link the sides of the DNA double

                     helix. The base pairs resemble rungs in a coiled ladder.

                     The nucleotides are called adenine, thymine, cytosine and guanine; they

                     are abbreviated as A, T, C and G respectively. The bases form specific

                     nucleotide pairings, with A linking only with T, and C only with G.

                     Genes can have thousands of base pairs. The sequence and arrangement

                     of these base pairs create a genetic code.

                     Genes give coded instructions to the cell on how to assemble proteins.

                     The making of a protein from this code is called gene expression.

                     Many human disorders are caused by genetic flaws, or by the absence of

                     one or more genes. Once a gene has been linked to a human disorder,

                     researchers hope to learn how to manipulate, correct or replace that

                     flawed gene, or the protein it expresses, to treat the disorder.

                     Even after all genes are identified, it will take many years before science

                     fully learns how to use this knowledge to predict and diagnose illnesses,

                    and to develop and test drugs and other new medical treatments. AP

Category: 32. Genome Project and Genomics