Figure 1.

Cytogenetic analysis of some selected w⁺ reversions of w^m4 described in text. (a) w⁺⁽⁷⁾/w^m4 female; the w⁺⁽⁷⁾ chromosome is a reinversion of w^m4 and pairing occurs between 3C and 20F. As a result, the telomeric regions 1–3C appear at both sides of the X chromosome (arrows); 20F is on the left side of the picture. The arrowheads indicate the breakpoints in 3C. (b) w⁺⁽⁷⁾/Y male; the X chromosome shows the banding pattern of wt at the w⁺ locus (arrowhead). (c) w⁺⁽¹¹⁾/w^m4 female; the w⁺⁽¹¹⁾ chromosome is also a reinversion. Here, the pairing occurs only at the telomeric region. Starting from 3C (arrowhead), the two homologues separate from each other over their entire length up to the chromocenter (arrows). (d) w⁺⁽²¹⁾/w^m4 female; the w⁺⁽²¹⁾ chromosome has the same sequence as w^m4 with pairing along the entire length. However, at 3C1–2 (arrowhead), the difference between the two homologues is evident. This explains the visible small loop.