We have written this short entry to provide a general overview about the concept of heritability and the basis for it in ADNTRO, as a recent addition to the health report, where we provide either (1) “trait heritability” or (2) “SNP heritability”.
The definition of Heritability is “a measure of how much of the variation of a trait can be attributed to variation of genetic factors, as opposed to variation of environmental factors”.
“H” or heritability is a fundamental parameter in genetics. First introduced by Sewall Wright and Ronald Fisher nearly a century ago, it is key to the response to selection in evolutionary biology and to the prediction of disease risk in medicine.
Trait heritability vs SNP heritability
In the case of ADNTRO we make an additional distinction between the heritability of the trait as a whole or to the genetic markers (SNPs) associated with it. This distinction is subtle, but very relevant.
Imagine we assume that our biology can be explained as a function of our genes + our environment*. Genome Wide Association studies (GWAS) are powerful genetic studies that help understand the heritability of specific traits – Using basic yet powerful statistical methods, we can estimate the variability of a phenotype attributable to genetic effects, nonetheless, when we estimate the predisposition to a specific disease only the most relevant SNPs are included in the analysis and therefore the % of heritability “explained” is lower. Basically, at ADNTRO we want to provide this information to help you pounder how big/small is the genetic factor when explaining your predisposition.
To give you a best feel for it, the heritability of a trait such “eye color” is very high (almost 100%) since the proportion of the variation in eye colour within a population explained by the environment or random chance is mostly Zero, but other traits can be surprisingly high or low when compared to our own expectations.
Genetic factors and their contribution to the different traits
Below, we can see the comparison between what people think about the heritability of specific traits-in gray in the graph-and the results of genetic research on it-in red in the graph. (Source: Robert Plomin research) that produce a meaningful discussion on the 2018 article «The stability of educational performance in the school years is largely explained by genetic factors» (Nature Journals) and that we also explain in another article about his book «Blueprint«.
Sources used by ADNTRO for reported heritability
The main sources used in ADNTRO for heritability are as follows (estimated or explained) have been based on data from the study itself on which we base our results (since these studies generally report an estimate of H) and the great laboratory from Neale Lab that provide statistics for these studies, mostly based on UK Biobank data.
Finally, we would like to point out that there are multiple and important nuances in the concept of heritability (broad and narrow definitions, multivariate... ) that require further reading. This Wikipedia article is very well detailed and complete. If you would like to read more about this term, two additional recommendations: (1) a very nice article written by Pedro De Bruyckere («Who is best at guessing the heritability of traits (men/Women)) and (2) “Heritability in the genomics era — concepts and misconceptions» (Nature Journals).
*Mathematically there is an additional factor to take into account, and this is the Covariance for GxE (the way Genes and environment interact with each other).