Molecular Biology

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Abstract

The challenge of correlating lifespan with genetics, is that “genotypes are generally gathered from living persons, whereas lifespan (total elapsed time between birth and death) is a property of deceased persons. Due to this challenge, current age has been used as a lifespan proxy trait in many human aging studies.” However, as decades go by and additional studies are done using age as a lifespan proxy, there will be confounding factors having to do with such things as the advancement of medicine or increases in pollution.

AncestryDNA offers genealogical DNA tests to consumers. Consumers can choose to allow their results to be used in research. By combining the data from AncestryDNA and an independent UK Biobank, the maternal and parental lifespans were compared with the genetics of the living DNA donors.

While it is difficult to measure the genetic contribution to variation in human lifespan, the estimation is that the heritability effect of lifespan is under 10 percent. One confounding factor is social inheritance, where people are born into social factors that can contribute to better health or lifespan. Another confounding factor is assortive mating, a form of sexual selection where individuals that have similar appearance tend to mate with each other more frequently than if the mating was random (birds of a feather flock together).

Different races have different life expectancies, not only because of genetics, but also the socioeconomic factors they are born into. Isolating and quantifying the contributions to lifespan from these types of counfounding variables is not possible with current methods.

Phenotypes such as lifespan are influenced by more than one gene. Looking individually at each gene that affects lifespan, there are gene variants. Some of these variants result in the same phenotype, while some can cause differences in lifespan. The ones that do not cause differences are often grouped together, or classified as the same gene type, or allele.

Variants where a single nucleotide in the DNA is altered often result in the same phenotype. These single nucleotide differences are referred to as SNP (single nucleotide polymorphism) variants. SNP's can arise in any of the cells of the body due to mutations. While mutations are infrequent, they occur because the DNA copying process is imperfect.

As a population grows older, members of the same age with alleles that reduce lifespan, will die off first. The cells within an individual also mutate, but at a very slow rate. So slow, that DNA samples from the same person, taken 80 years apart, would still show a majority of cells having the original DNA.

There may be some cases, however, where mutations have a survival advantage compared to neighboring cells, and are able to gain majority. An example of this is cancer. However, this phenomena is not relevant to this study.