Figure 2. The behaviour of the chromosome 3H^ch homologues during pachytene.

Telomeres, subtelomeric regions (first line) and centromeres (second line) of the two homologues are indicated by a white arrow. Solid and broken lines in the diagrams represent the paired and unpaired regions of the homologous chromosomes, respectively. (a) In the line carrying the version of chromosome 3H^ch in which a deletion on the long arm has removed neither the long arm telomere nor the subtelomeric region, the two homologues are fully paired, while (b) in the line carrying the version of chromosome 3H^ch in which a deletion on the short arm has removed the subtelomeric region, they are only associated along the distal region of the long arm, leaving the centromeric region and the short arm unpaired. (c) At a later stage during meiosis, pairing is extended in the line carrying the version of chromosome 3H^ch in which a deletion on the short arm has removed the subtelomeric region. The homologues are fully associated along their long arm and the pairing signal has been transmitted through the centromeres, although the short arms remain largely unpaired. (d) At an even later stage, the homologues become fully associated. Bar: 10 µm.