Solovei I, Gaginskaya E, Hutchison N, Macgregor H
Biological Institute, University of St Petersburg, Russia.
Chromosome Res. 1993 Sep;1(3):153-66. doi: 10.1007/BF00710769.
The ZW bivalent has been identified and characterized in detail in its lampbrush form in oocytes of chicken, quail, turkey, pigeon, chaffinch and sparrow. The sex bivalent in all six species looks like a single highly asymmetrical chromosome. Most of it has the typical lampbrush organization. The terminal one-fifth is relatively thick and condensed and bears only a few pairs of lateral loops: this condensed terminal region is the W chromosome; the part with normal lampbrush morphology is the Z. The two are connected by a single near terminal chiasma. The fine scale morphology and arrangement of loops and markers on Z and W chromosomes are described for each species and lampbrush maps have been constructed. The identification of the lampbrush sex bivalent is based on the following criteria. The asymmetrical chromosome has two centromere regions. In the interstitial region of the asymmetrical chromosome where the junction between Z and W chromosomes is supposed to be, there are telomere-specific loops and telomeric DNA sequences and there is good morphological evidence for the presence of a chiasma. There are W chromosome specific DNA sequences in the region of the asymmetrical lampbrush chromosome that is thought to represent the W. Breed-specific variations in the morphology of the chicken W chromosome with respect to the sizes, numbers and arrangements of axial chromomeres and distributions of specified repeated DNA sequence families have been identified, offering one of the first examples of definitive correlation between a repeat family and a single chromomere. The lampbrush chromosomes of all the birds examined, except quail, terminate in distinctive free hanging loops. These are a novel feature in the sense that at the end of each chromatid there is a large transcription unit terminating in a cluster of telomeric DNA sequences.
ZW二价体已在鸡、鹌鹑、火鸡、鸽子、苍头燕雀和麻雀的卵母细胞中以灯刷形式被详细鉴定和表征。所有这六个物种中的性二价体看起来像一条高度不对称的单染色体。其大部分具有典型的灯刷结构。末端的五分之一相对较粗且浓缩，仅带有几对侧环：这个浓缩的末端区域是W染色体；具有正常灯刷形态的部分是Z染色体。两者通过一个近末端交叉相连。描述了每个物种Z和W染色体上精细尺度的环形态和排列以及标记，并构建了灯刷图谱。灯刷性二价体的鉴定基于以下标准。这条不对称染色体有两个着丝粒区域。在不对称染色体的中间区域，即Z和W染色体连接处所在的位置，存在端粒特异性环和端粒DNA序列，并且有良好的形态学证据表明存在交叉。在不对称灯刷染色体中被认为代表W的区域存在W染色体特异性DNA序列。已鉴定出鸡W染色体在轴向染色粒的大小、数量和排列以及特定重复DNA序列家族分布方面的品种特异性形态差异，这是重复家族与单个染色粒之间明确关联的首批例子之一。除鹌鹑外，所有被检查鸟类的灯刷染色体都以独特的游离环结束。从每个染色单体末端都有一个以端粒DNA序列簇结束的大转录单位这一意义上来说，这些是一个新特征。
