My mum, and her mum were both emet too, but my sister is not at all. I don't think it's 'genetic' but I think the reaction that parents have when it's happening (e.g. calm and normal versus psycho emet panic!) REALLY affects kids in terms of whether they see being sick as ok or terrifying. I'm going to try SO hard to stay calm and rational with my kids to try and break the chain, because life must be so much easier without this!