Tail bleeding time assays. Offspring produced from GP Ibβ^Het × GP Ibβ^Het crosses were subjected to tail bleeding time assays prior to their genotyping. Results are shown for 5-week-old animals and the cessation of bleeding time was recorded. Four animals, later genotyped as GP Ibβ^Null, failed to stop by bleeding by 10 minutes, at which point the tail was cauterized. Shown are the data obtained from individual animals.