Chromosome banding in Amphibia. XIX. Primitive ZW/ZZ sex chromosomes in Buergeria buergeri (Anura, Rhacophoridae).
The karyotype of the common bell-ring frog, Buergeria buergeri, is characterized by primitive ZW/ZZ (female/male) sex chromosomes. The only difference between the Z and W is the presence of a nucleolus organizer region (NOR) and its associated constitutive heterochromatin in the Z. This causes a sex-specific difference in the number of ribosomal RNA genes, with a male:female ratio of about 2:1. In the cell nuclei of the various tissues analyzed the NORs on both Z chromosomes are transcriptionally active. During meiosis in females, the ZW chromosomes form a characteristic lampbrush sex bivalent with a conspicuous absence of chiasmata along half of their long arms. No further morphological differences are present in these primitive sex chromosomes. The results indicate that there is no Z-chromosome inactivation mechanism operating in this amphibian. Experimental sex reversal of genetic (ZW) females to functional males was achieved by estrogen treatment of tadpoles. Mating of sex-reversed females with normal females yields the expected 25% lethal nucleoli-less WW embryos, which die at the tail-bud stage. The sex of the remaining viable embryos with one or two nucleoli determined after metamorphosis was in a female:male ratio of 1.57:1. These genetic experiments confirm that a primitive ZW/ZZ (female/male) type of chromosomal sex determination operates in this species.
Schmid
M
M
Department of Human Genetics, University of Würzburg, FRG.
Ohta
S
S
Steinlein
C
C
Guttenbach
M
M
D000818:Animals; D001001:Anura / Q000235:genetics*; D002466:Cell Nucleolus / Q000648:ultrastructure; D002871:Chromosome Banding; D004275:DNA, Ribosomal / Q000235:genetics; D012734:Disorders of Sex Development; D004625:Embryo, Nonmammalian / Q000648:ultrastructure; D005260:Female; D007399:Interphase; D007621:Karyotyping; D008297:Male; D009697:Nucleolus Organizer Region / Q000648:ultrastructure; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D012339:RNA, Ribosomal, 28S / Q000235:genetics; D012730:Sex Chromosomes / Q000648:ultrastructure; D012732:Sex Determination Analysis
D004275:DNA, Ribosomal; D012337:RNA, Ribosomal, 18S; D012339:RNA, Ribosomal, 28S