Immortalized Cell Lines: Their Creation and Use in Gene Mapping

Unequivocal physical ordering of genes and genetic markers along chromosomes has been an essential component of gene mapping for much longer than the span of the current genome mapping effort. Human geneticists contemplate mapping a gene as soon as its presence can be identified either directly at the DNA level or through its product (RNA, protein, or even an abnormal disease state). Unlike the situation in the mouse, physical rather than genetic mapping is the method of first choice. Accurate chromosomal localization is usually a multistep process starting first with assignment to one of the 23 chromosomes, and progressing to increasingly refined subregional localization. Somatic cell hybrids and in situ hybridization (see Chapter 25 ) have been the techniques most often used.