Figure 3.

KYS maize pachytene chromosome squash. (A) By phase microscopy, large interstitial knobs (arrowheads) on the unstained chromosomes are visible along with smaller terminal knobs (small arrows). Pericentric heterochromatin is visible as darker segments of bivalents that are often about one-third of the length of each bivalent, e.g., observe the bivalent at the lower center. (B) The same squash after DAPI staining. Knobs are prominent bright blue enlargements along bivalents indicating a high concentration of DNA in knobs. Pericentric heterochromatin is also brighter than the distal euchromatin indicating higher concentrations of DNA in pericentric heterochromatin (but less than in knobs). (C) The same squash after FISH with the 180-bp knob repeat (red). Large interstitial knobs (arrowheads) and the smaller terminal knobs (small arrows) are specifically labeled with the 180-bp repeat probe. Bar, 5 µm.