Hello. According to an article in Science News (Mar 7, 2004?): Mammals with an XX set of chromosomes become female. Those with XY become male. The Y chromosome is much smaller than the X. Birds with a ZZ set of chromosomes become male. Those with ZW become female. The W chromosome is much smaller than the Z. My question: Which chromosomes determine sex in a mollusk? Is it simple to see, as in birds and mammals, or does it depend on individual genes on one or several chromosomes? Is there a general rule for all mollusks, or do different species sex out differently? Thank you. Mark Wood, Nanakuli, Hawaii.