ABSTRACT
Complementation analysis based on somatic cell hybridization has also proved very useful for the identification of dominant and recessive genetic events in the control of a range of biological processes. Complementation analysis by cell fusion studies has demonstrated genetic heterogeneity within XP and has provided evidence for the existence of at least seven excision-deficient complementational groups: XPA–G and a group called XP-variant. The mutants were all recessive and were divided into five complementation groups, with the mutants affected mainly in the expression of major histocompatibility class II and invariant-chain genes. In order to identify the chromosomes involved in regulating cell proliferation, single human chromosomes were introduced into immortal human cells representative of the different complementation groups. Interspecies microcell hybrids, containing a single human chromosome or part of a chromosome with suitable selectable markers, have facilitated the regional mapping and cloning of a number of genes.
