So today’s question is the following! (First part is deleted as it is just spelling/grammar problems on my website and I thank you for pointing it out to me!
Also, i have a question. Have the recent DNA haplogroup publications been of any relevance to jews? As far as i know, you inherit from your mother, and one is really a jew if their mother is a jew (correct me if im wrong). I however found numerous people online trying to associate jews to Y-DNA chromosomal studies, which is the paternal chromosome only passed on by the male. Should jews not be lookng at merely the mT- DNA (maternal) chromosome? If so, is there a mT – DNA that has been associated to true jews? Or can jews be from many different mT haplogroups? Since if true jews were only by birth of their jewish mother, than that would mean all jews have the same mT haplogroup in their DNA.I will use the term “true Jew” to refer to the above compared to my answer. It is not written as an insult.
Checking if you are Jewish via genetics is both an interesting question but also one with no “useful” answer but let me explain. You are correct in saying that someone is Jewish if their mother is Jewish (at least to Orthodox Judaism and some other point of view as Reform Judaism tends to agree it can be either parent) but it isn’t the only way to become Jewish.
It is possible to convert to Judaism and avoid having any common genetic material that other Jews may have. You are however correct-ish on the last line. If we assume all ” true Jews” are via the mother only then you would only need to look for common genes. However, that logic assumes no one converts to Judaism, no baby is adopted into a family and so on.
To answer the question you would be correct in it would make sense to compare the mother’s bloodline rather than the father’s but this is something that varies on the question “who is a Jew”.
TL’DR answer: Many Jews will have genes in common however not every single Jewish person was born into Judaism from their mother with many having converted, adopted and such.
Kyle ben Avraham Avinu (קייל בן אברהם אבינו) (2019) Common Genetics and Judaism. [online] Ask a Jew. Available at: https://askajew.co.uk/question/common-genetics-and-judaism/ [Accessed 14 Nov 2021]