My partner is waiting on her DNA results. She strongly suspects that her 2nd cousin is her father (long story).

Will the DNA results reveal the possibility from more concentrated markers, or less genetic diversity?

Is it even something that will be picked up on the report?

Do the reports even suggest a possibility of very close inbreeding within a family?

  • 3
    I expect the downvotes are because it is not obvious exactly what your question is. If I'm understanding correctly, you have a DNA test for your partner, but not one for the second cousin, and you want to know if/how this may or may not be helpful in determining her parentage? I would start by including some details of which test your partner has taken (each company varies in how much detail they will give you).
    – Harry V.
    Jan 13, 2018 at 23:34

2 Answers 2


A person will share roughly 3% of their DNA with a second cousin. A person shares 50% of their DNA with their father. If you have the luxury of testing the autosomal DNA of both the person and the second cousin, then that will obviously give you the answer. However, I expect that is not the case.

If any other close relatives (siblings, parents, aunts/uncles) of the second cousin have tested, this could also give you an answer – you would expect to have a stronger match with these people if your second cousin is also your father. If you have the opportunity to test other family members (on both sides of the family), I would encourage you to do so, as this will help narrow down any genetic matches to one side of the family.

Ethnicity percentages will be a quite unreliable and subjective means of drawing a conclusion, and would only really be helpful if your second cousin/father had a particularly unique genetic history compared to the rest of your family (i.e. ancestry recently from another continent). If not, then I would tend to ignore ethnicity percentages for this purpose.

A child born between two second cousins would not, in most people's estimations, be considered "close inbreeding" (I have a number of first cousin marriages in my family tree). However, there are tool available that may be able to detect such a relationship based on the results of an autosomal DNA test. Each chromosome has two alleles. If a person has significant areas on each allele that are identical (runs of homozygosity) then this would be indicative of one's parents being related. Gedmatch has a tool call Are Your Parents Related? which tests for this.

  • Thankyou for your answer. Your assumptions are correct. The suspected father/2nd cousin is believed t be dead, and it would be hard to chase up remaining members of their family, and quite delicate to try and persuade them to have a DNA test without it creating uncomfortable questions. What you mention about the autosomal DNA test sounds like it will be able to resolve this. My partner has taken the test with DNA Heritage. Thank you so much for your help!
    – RosarioC
    Jan 14, 2018 at 10:32
  • Just to clarify, it's her mother's first cousin, and her own (my partner's) second cousin.
    – RosarioC
    Jan 14, 2018 at 10:37

Just make so-called atDNA test. It is called 'familyfinder' in terms of FTDNA laboratory. Yoy will be able to make correct suggestion based on the total shared amount of DNA

  • 1
    Update: I uploaded my DNA report to Gedmatch and did the test. Her parents aren't related! Yay! DNA rocks.
    – RosarioC
    Jan 26, 2018 at 22:44

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