Figure 1.

Illustration of the relationship between the parental alleles and the amplified ones of an oncogene. (a) In a cancer cell, a gene that locates at chromosome 8 (yellow dots) has two amplified copies located on one of the two 8^th chromosomes, either the paternally or the maternally derived one. Moreover, the gene also has an amplified copy on each of the two 10^th chromosomes and two copies on one of the two 12^th chromosomes (red dots). Aneuploid chromosomes with amplified oncogenes often appear in cancer, but are not illustrated here. Although the cell shows increased expression of this gene, relatively to the normal cells, it is difficult to pinpoint which one or ones of these eight (two normal and six amplified) alleles are responsible for the excess of the RNA transcripts. (b) If both of the gene (red bar) and its promoter (short yellow bar) at chromosome 8 are amplified and the amplified copy is translocated to one of the 10^th chromosomes, the co-amplified promoter may allow the amplified allele to be activated, and thus overexpressed, in a way similar to the activation of the parental allele(s)