To understand this link, I did the common sense thing of going to the following information on the site. From tab “About Genetic Geneology”
“Genetic genealogy or genetic ancestry testing is the use of DNA to study ancient origins and relatedness between individuals. When combined with traditional paper genealogy, it is a powerful tool for the genealogist’s toolbox. There are four types of genetic ancestry testing: Y-chromosome, X-chromosome, mtDNA, and autosomal DNA test.”
“Genetic” scientists, including paleoanthropologists, have a toolbox of thousands and thousands of genes and billions of chemical base pairs. Human descendants of Adam and Eve are determined by their entire genome. An additional valuable piece of information is that each individual carries two copies or versions of a gene. The term for these versions is alleles. Alleles develop in a natural way, that is, there can be tiny changes or major changes in the original gene over extended periods of time. In turn, alleles can also change. At conception, the child receives one copy of a particular gene from each parent. With some imaginative thinking, it is easy to understand that by now there could be hundreds of existing alleles of the DRB1 gene.
Applying these basic concepts to real descendants of Adam and Eve, it is entirely possible that a child could receive an allele of a particular gene, for example the DRB1 gene, which developed only a few hundred years ago, well after the appearance of Adam and Eve. What needs to be noted is that the DRB1 gene is part of the human immune system which is integral to human nature. Catholicism directly teaches that Adam had a true human nature. Therefore, it is proper to say that current humans inherited their general immune system from Adam, albeit there were numerous alleles since the dawn of human history.