Even if Abraham _did_ exist, at this point in time it's like trying to distinguish a drop of water from the ocean it's now living in. That's how little would have remained of Abraham's DNA so much later.
If this were true, genetic testing wouldn’t be able to identify folks as Ashkanazi Jewish, for instance. But it can. And many phenotypes do the same.
I was replying to the claim that Abraham's DNA (if he existed) could be traced in today's Jewish population. And that _is_ impossible.
In any case, it's not like you identify Ashkanazi Jews from DNA, instead it's that when DNA-checking people who self-identify as Ashkanazi then you find Middle Eastern ancestry. To recite Wikipedia's citation: '.. while certain detectable Middle Eastern genetic components exist in numerous Jewish communities, there is no evidence for a single Jewish prototype, and that "any general biological definition of Jews is meaningless"'