def getNbVariants(self, x1, x2 = -1) :
		"""returns the nb of variants of sequences between x1 and x2"""
		if x2 == -1 :
			xx2 = len(self.defaultSequence)
		else :
			xx2 = x2
		
		nbP = 1
		for p in self.polymorphisms:
			if x1 <= p[0] and p[0] <= xx2 :
				nbP *= len(p[1])
		
		return nbP
returns the nb of variants of sequences between x1 and x2