This 2019 rodent study by the Washington State University labs of Dr. Michael Skinner continued to F₄ generation great-great-grand offspring, and demonstrated that epigenetic inheritance mechanisms are similar to imprinted genes:

“Epigenetic transgenerational inheritance potentially impacts disease etiology, phenotypic variation, and evolution. An increasing number of environmental factors from nutrition to toxicants have been shown to promote the epigenetic transgenerational inheritance of disease.

Imprinted genes are a special class of genes since their DNA methylation patterns are unchanged over the generation and are not affected by the methylation erasure occurring early in development. The transgenerational epigenetic alterations in the germline appear to be permanently reprogrammed like imprinted genes, and appear protected from this DNA methylation erasure and reprogramming at fertilization in the subsequent generations. Similar to imprinted genes, the epigenetic transgenerational germline epimutations appear to have a methylation erasure in the primordial germ cells involving an epigenetic molecular memory.

Comparison of the transgenerational F₃ generation, with the outcross to the F₄ generation through the paternal or maternal lineages, allows an assessment of parent-of-origin transmission of disease or pathology. Observations provided examples of the following:

1. Pathology that required combined contribution of both paternal and maternal alleles to promote disease [testis and ovarian disease];
2. Pathology that is derived from the opposite sex allele such as father to daughter [kidney disease] or mother to son [prostate disease];
3. Pathology that is derived from either parent-of-origin alleles independently [obesity];
4. Pathology that is transmitted within the same sex, such as maternal to daughter [mammary tumor development]; and
5. Pathology that is observed only following a specific parent-of-origin outcross [both F₄ male obesity and F₄ female kidney disease in the vinclozolin lineage].”

https://www.sciencedirect.com/science/article/pii/S0012160619303471 “Epigenetic transgenerational inheritance of parent-of-origin allelic transmission of outcross pathology and sperm epimutations”

This study showed that epigenetically inherited legacies extend to the fifth generation. Do any of us know our ancestors’ medical histories back to our great-great-grandparents?

Will toxicologists take their jobs seriously, catch up to current science, and investigate possible effects in at least the F₃ generation that had no direct toxicant exposure?