Position effect variegation of eye color in Drosophila

(a) The w+ allele is expressed in wild-type X chromosomes. Markers indicate the hetero-chromatin compaction region. (b) It is also expressed in inverted X chromosomes as long as the centromeric heterochromatin does not spread to cover the gene. If the spread of centromeric heterochromatin covers the new gene location in inverted X chromosomes, w+ is silenced(a) The w+ allele is expressed in wild-type X chromosomes. Markers indicate the hetero-chromatin compaction region. (b) It is also expressed in inverted X chromosomes as long as the centromeric heterochromatin does not spread to cover the gene. If the spread of centromeric heterochromatin covers the new gene location in inverted X chromosomes, w+ is silenced

(a) Wild-type eye color — Telomere Heterochromatin (less compacted) w (more compacted) (b) Variegated eye color Inversion moves W+ near the centromere. Centromeric heterochromatin pread is variable. U1