JustinWyllie

Hi This is a beginner question. I'm interested in ADHD though the question is a general one. For example, the Cardiff genome study, found a genetic correlation to ADHD behaviours. But they also found that this genetic factor was equally present in boys and girls. Could there be a genetic factor for ADHD which boys carry more than girls? I understand that this may be the case if the genetic factor in question is on the X-chromosome. Is there any other case where this could be the case? Many thanks --Justin Wyllie

Ok. Thanks. It is much clearer now. I think you mean (MZc-DZc)*(MZg/DZg)=genetic component of the trait ? I think you are just testing me?

Hi dmaiski Thanks. So can I just check? In the first study (when we thought that the random assumption could be made) the maths looks like this: Environmental contribution = 1 - ((.8-.4)*(1/.5)) = 0.2 Once we corrected for 75% shared genes in the dz set: Environmental contribution = 1 - ((.8-.4)*(1/.75)) = 0.47 So the corrected figure is that in this study the environmental contribution is higher than when we mistakenly assumed 50% shared genes in the dz group? And, sorry, but can you explain the 1 - in the equation? Is that just 'not the genetic contribution'? Many thanks again --JW

Hi I am trying to understand twin studies and really coming up against a brick-wall, probably because of my lack of maths knowledge. In particular I am trying to understand how making the "random mating assumption" when it should not be made (i.e. for the trait being studied random mating does not hold) could effect a study. For example in an imaginary study: In the mz set lets say there is a concordance factor of 80%. In the dz set 40%. The random mating assumption has been made. However; in fact for this trait the random mating assumption should not have been made, it turns out, and in fact the dz group shared 75% of their genes not 50%. (This is an artificial example probably exaggerated). I *think* that that means the genetic effect in this case would have been exaggerated. But I am struggling to understand this and to show it mathematically. Am I right and can anyone explain it to me? Many thanks --Justin Wyllie