Molecular Genetics

Facts

• Somatic hybrids are formed by fusion of cells. Cultured cells from two different species can be induced to fuse to form hybrid cells whose nuclei also fuse (heterokaryons).
• In interspecific fusions, selective loss of one parents' chromosomes occurs during propagation of the fused cells. When mouse-human hybrid cells are cultured they loose many of the human chromosomes.
• Hybrid cell lines A, B, and C contained the human chromosomes indicated in the table below.
• The cell lines were tested by enzyme electrophoresis for their ability to make the human hypoxanthine phosphoribosyl transferase (HPRT) , glucose-6-phosphate dehydrogenase (G6PD) and thymidine kinase (TK).
• Since the extra chromosomes are not essential, they often undergo deletions of parts of the chromosome, revealed by chromosome banding.

Interpretations

• HPRT and G6PD genes are located on the X chromosome, while the TK gene must be on chromosome 17.
• HPRT and G6PD are part of a linkage group containing other genes. These other genes must also be located on the X chromosome. For example, phosphoglycerate kinase, known to be linked to glucose-6-phosphate dehydrogenase is also on the X chromosome.
• Identification of the chromosome location of one gene is sufficient to assign the whole linkage group to that chromosome.
• Correlation of the breakpoints in a chromosome deletion series with the presence or absence of the enzyme can be used to assign the gene for the enzyme to a specific chromosome band.

Further information

• Large collections of cell lines containing different human chromosomes or parts of chromosomes have been established.

This is page 1213 of Molecular Genetics by Ulrich Melcher, © 1997, 1998