The <i>DcY(H1)</i> chromosome and BARTL assay.

<p>Chromosome breakage and telomere loss in the BARTL assay. The <i>DcY(H1)</i> chromosome (drawn as sister chromatids in G2) is a <i>Y</i> chromosome that carries <i>y</i><sup><i>+</i></sup> on the short arm and dominant <i>B</i><sup><i>S</i></sup> on the long arm. Inverted <i>FRTs</i> are inserted proximal to <i>B</i><sup><i>S</i></sup>. The centromere is represented as a solid black circle, the telomeres as green rectangles, <i>B</i><sup><i>S</i></sup> gene as a red rectangle and inverted <i>FRTs</i> as half-arrows. When FLP mediates unequal sister chromatid exchange between inverted <i>FRT</i>s a dicentric and an acentric chromosome are produced. In the subsequent mitotic anaphase the dicentric chromosome is pulled to opposite poles and usually breaks. Each daughter cell receives a chromosome with a single broken end and one or both daughter cells lose the <i>B</i><sup><i>S</i></sup>-containing acentric fragment.</p>