In vitro platelet aggregation. For these assays, blood was pooled from 6 to 8 male mice. Platelet aggregation was induced by addition of collagen (2 μg/mL) (left panel) or 10 μmol/L ADP (right panel). When exposed to ADP, no difference in the extent of aggregation was observed (right panel). When stimulated with collagen (2 μg/mL) (left panel), aggregation of platelets from Gp6^−/− SHORT mice (17 ± 5%; mean ± SD) or Gp6^−/− LONG mice (14 ± 2%) was comparable and significantly lower than that seen in wild-type littermates (62 ± 7%; P < .01 in both cases). The mean (± SD) for 3 separate assays is shown.