Chromosome Linked to Diseases Is Mapped

British scientists have mapped chromosome 20, the third and longest chromosome to be sequenced in the Human Genome Project. Chromosome 20 is best known for harboring genes that contribute to forms of the brain-wasting Creutzfeldt-Jakob disease and severe-combined immunodeficiency, an illness in which the immune system is crippled. Chromosome 20 contains 727 genes and accounts for about 2% of the total human genetic material, the team reported in the Dec. 20 issue of Nature.

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Compiled by Times medical writer Thomas H. Maugh II