Birth Era Affects Gene Expression: An observer effect in genetics

The scientific explanations for human folly can no longer be attributed solely to nature and nurture. Time has wound its way in, leaving its mark on generations.

A recent study published on January 13 in the Proceedings of the National Academy of Sciences has revealed an unforeseen connection between global change and the phenotypic expression of genetic traits. The study, which reviewed obesity research over time, found that observed genotypic-phenotypic relationships can be attributed to the time period when the study was conducted, as well as to the years in which participants were born. Scientists now suggest that the genotype-phenotype relationship might not be so straightforward, because the context of observing this data seems to influence the data itself.

A man born before 1942 (left) has the same genotype as a man born after 1942 (right), but birth era has altered the expression of genes. Whole environment can have an impact on genotype-to-phenotype translation, according to a recent study. Image courtesy of Authority Nutrition.


“We were able to show that whether or not an allelic variant has an effect on a phenotype depends on the historical period during which the subjects were living or the research was conducted,” said Nicholas Christakis, a co-author of the study and Yale professor of ecology and evolutionary biology.

One of the first of its kind, the study used the FTO, or fat mass and obesity associated gene, to observe the effects of birth cohort on body mass index (BMI). Using data collected through the Framingham Heart Study, Christakis and his colleagues identified individuals with the FTO gene and plotted their BMI against their birth era. Surprisingly, individuals born prior to 1942 demonstrated no stark difference in BMI across three genotypes. Meanwhile, those born after 1942 had statistically significant differences in BMI depending on the allele present.

“The effects of genes are historically contingent. There is a gene-by-environment interaction at the level of the whole environment,” Christakis said.

This study indicates that the connections between nature and nurture run deeper within our nuclei than previously thought.  The authors of the study believe that the results can be explained by environmental and societal factors that influenced the expression of the FTO gene.

This study also serves as a warning for future research. “Our study is not about obesity; it is about something broader” Christakis said. The research implies that depending on when researchers conduct a study and who they use as subjects, certain relationships between genotype and phenotype may or may not be found.

An important scientific principle applicable here is the observer effect, which states that the simple act of observing a phenomenon changes it. By studying the correlation between genotype and phenotype during a certain time period, scientists inadvertently influence this relationship and leave room for uncertainty.

Cover image: A recent study co-authored by Yale professor Nicholas Christakis used BMI to study the relationship between a genes, obesity, and birth era. Image courtesy of Fresh Start Health.