G-Banding of Chromosomes from Chorionic Villi
Examine the slide using an x 40 phase-contrast objective and record the position of a suitable metaphase (Fig. 1 a).
Transfer the slide to a staining rack and flood with 10% hydrogen peroxide for 3–5 min. (If the preparation is several days old, 30 s peroxide pretreatment is sufficient.)
Rinse off the peroxide with isotonic saline and flood with dilute trypsin.
Relocate the metaphase and examine the morphology of the chromosomes during the trypsin treatment.
As soon as the chromatids become well defined with a rounded three-dimensional appearance (Fig. 1 b), the slide is returned to the staining rack and flooded with stain (Leishman’s or Giemsa, appropriately diluted with 6.8 Sorensen’s buffer).
Rinse off the stain with buffer, blot dry, mount and examine (Fig. 1 c).