Heritability: a story from the bathroom

Since last summer, I have been working on the ‘heritability (h2)’ for almost half year, it’s defined as the proportion of the phenotypic variance of human disease or complex traits attributed to genetic effects. There were many different concepts made me so confused, but one day when I had shower, I found it could be explained from the analogy of showerhead. psb

We can take the ‘missing heritability’ as the phenomenon that the temperature of the water sprayed from the shower head was too cold compared with those in water heater (just 5-10% h2 can be explained by significant associated loci from genome-wide association studies) even we have turned off the cold valve to stop the cold water and just kept hot water (just focus on additive genetic effects), previous studies mainly focused on how to find the problems in the shower head (why SNPs cannot explain all the total h2), such as undiscerned rustiness that impede the water flow (untagged rare variants, et al), or the pipe connecting shower head and water heater cannot keep warm very well, heat would run away very easily (imperfect linkage disequilibrium, et al); limited studies or comments argued another explanation from the possibility that cold water was still introduced (total h2 was overestimated), perhaps because certain cold water was introduced in the pipe of hot water (epistasis), our study indicated that perhaps the problem also could occur at the valve to stop cold water, although cold water was stopped in our naked eye (previous twin study with small samples), if using clairvoyant glasses (sample size was large enough), we could find that the hot water was still mixed with cold water, and this time, we can completely stop the cold water (disentangle the mixed A and D). However, this situation would not always happen in different shower head (just like we also haven’t identified any D components for some traits).



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