Fig. 2. GalT I-null sperm do not require capacitation in vitro to achieve maximal binding to the zona pellucida. Wild-type (gt +/+) and GalT I-null (gt –/–) sperm were capacitated for varying amounts of time before incubation with ovulated eggs. The binding of GalT I-null sperm to the zona pellucida is independent of capacitation in vitro, whereas wild-type sperm show a capacitation-dependent increase in their ability to bind the egg. Each bar represents the mean±s.e.m.; n=3 experiments. In a single experiment, the value for each data point represents the average of three determinations. Thus, each bar reflects data from nine assays, each containing 30-40 eggs. The average number of sperm bound to eggs at 0 minutes was: wild type, 8±0; GalT I-null, 25±2; at 15 minutes: wild-type, 14±2; GalT I-null, 25±4; at 30 minutes: wild-type, 19±5; GalT I-null 25±2; and at 60 minutes: wild type, 19±2; GalT I-null, 21 ± 2. In each experiment, this value was normalized to fully capacitated sperm (60 minutes of capacitation is equivalent to 100% bound), so that results from replicate assays could be compared. *P<0.01.