Figure 1.

Imprinted genes are expressed in a parental-origin-specific manner. In the center, a cell is depicted with a chromosome inherited maternally (red) or paternally (blue), and two imprinted genes. Gene A is transcribed from the maternal allele (green box and arrow indicating transcription) and repressed on the paternal allele (light blue box). In contrast, gene B is transcribed from the paternal allele (green box and arrow) and repressed on the maternal allele (light pink box). Uniparental embryos and embryos that are uniparental for a given chromosome have been used to show that imprinted genes are critical for development as well as to identify imprinted genes (see text).