title: Differential sex chromosome replication and dosage compensation in polytene trichogen cells of Lucilia cuprina (Diptera: Calliphoridae).
abstract: Non banded sex chromosome elements have been identified in polytene trichogen cells of Lucilia cuprina using Y-autosome translocations, C-banding and Quinacrine fluorescence. The X chromosome is an irregular granular structure while the much smaller Y chromosome has both a dense darkly stained and a loosely organised segment. The X and Y chromosomes are under-replicated in polytene cells but comparison of C- and Q-banding characteristics of sex chromosomes in diploid and polytene tissues indicates that selective replication of non C-banding material occurs in both the sex chromosomes. Brightly fluorescing material in the Y chromosome is replicated to such an extent that it consists of half the polytene element, while the C-banding material, which makes up most of the diploid X chromosome, is virtually unreplicated. Differential replication also occurs in autosomes. In XXY males, and in males carrying a duplication of the X euchromatic region, a short uniquely banded polytene chromosome is formed. It is suggested that in males carrying two doses of X euchromatin a dosage compensation mechanism operates in which genes in one copy are silenced by forming a banded polytene chromosome.
mesh_terms: D000483:Alleles; D000818:Animals; D002871:Chromosome Banding; D004261:DNA Replication; D004175:Diptera / Q000235:genetics*; D012729:Sex Chromosome Aberrations / Q000473:pathology; D012730:Sex Chromosomes / Q000502:physiology*; D014178:Translocation, Genetic