closet cult is right. Males grow noticeably faster and with greater internode space. You won't be able to tell the sex from the leaves. The fact that one is much broader than the other is a sign of heterozygosity. That is, though it may be the same strain it could easily have a dominant chromosome for broad leaves and some of the seeds did not get that chromosome and show narrow leaves from a homozygous recessive chromosome pair. This is pretty commonly seen in hybrids, since 100% indica or sativa, etc., tend to be homozygous and show constant characteristics from plant to plant. The more you mix the genetics the more random your phenotypical plant is gonna be. That's just off the top of my head, I think Jorge Cervantes does a better rundown, I just wish I had my copy on me.