Is there a different genetic relation strength through maternal vs paternal line? In other words:

  1. am I more related to my mother than to my father or are they exactly equal? Or another way to ask it is am I any less related to my mother's mother's mother than to my father's father's father?
  2. If I branch off my family tree through my maternal grandmother's mother (Gen N), then is my genetic connection to my paternal grandfather's father the same?

For the record and for those interested, I want to give a little more detail than is in Leah's answer. Leah's answer is a very good overview and has the important points that a beginning genetic genealogist needs to know. The real world, as always, is a little more complicated.

Our DNA is organized in three kinds:

  1. autosomal chromosomes (numbered 1-22)
  2. sex chromosomes (X & Y)
  3. the mitochondrial chromosome

Autosomal DNA is most of our genetic heritage, being about 93% of it (over all three kinds of DNA by length). It acts just as Leah has outlined: you get exactly half from each parent, but a variable amount from each of your four grandparents.

The sex chromosomes (which are almost all of the rest of the DNA) act differently, as they not only determine sex but their inheritance depends on the sexes involved. A female will have two X chromosomes, inheriting one from each parent in much the same way as for autosomal chromosomes. A male will have only one X, inherited from his mother, and will additionally have a Y chromosome, inherited from his father. A Y chromosome is only about one third the size of an X chromosome, and has even less than proportionately fewer genes. So overall a male inherits about 49.2% of his DNA from his father and the rest from his mother (instead of 50%/50%).

The mitochondrial chromosome is a real oddball. It is tiny, being only 0.0003% of the kinds of DNA. It doesn't reside in the cell nucleus (where all the rest of DNA is), and there are many identical copies of it in a cell. And it is inherited by a child only from its mother.

So, yes, to a first approximation we do get half our genetic inheritance from each parent, and a variable proportion from earlier generations. For genealogy, the most important additional consideration is that the X and Y chromosomes have special inheritance rules that are a bit different than the rest.

  • How much DNA would a female inherit from here mother and father, respectively, given the following: "So overall a male inherits about 49.2% of his DNA from his father and the rest from his mother (instead of 50%/50%)." – PWD Jun 27 '18 at 23:43
  • @PWD, a female gets 50%/50% (to several decimal places, since the only unequal part is the tiny mitochondrial chromosome). – RobertShaw Jun 28 '18 at 3:03
  1. You inherit exactly half your DNA from each parent. So, no, you are not more related to one parent or the other.

    However, it is unlikely for you to inherit exactly a quarter of each of your grandparents' DNA. Often, you inherit 20% to 30% from each grandparent, totaling 100%. This is because you inherit a random 50% of each parent's DNA, so you may get a little bit more from one grandparent than another.

    Moving back in time, you rarely inherit exactly 12.5% from each great-grandparent, or exactly 6.75% from each great-great-grandparent, etc.

  2. Per the above answer, you may inherit more or less DNA from your maternal grandmother's mother than from your paternal grandfather's father, or you may inherit the same amount. Eventually, though, you have ancestors that you have not inherited DNA from. If I remember correctly, this starts happening at around 6 to 7 generations.

I highly recommend reading "Genetic Genealogy in Practice" by Blaine Bettinger and Debbie Parker Wayne. Your local library may have a copy of it. The book has exercises at the end of each chapter (and answers in the back) to help cement the knowledge in the chapter.

  • Thank you. Extremely useful - both the explanation and the book reference. – PWD Jun 26 '18 at 15:25
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    @PWD btw, if you're trying to decide on a DNA test to take, check out "The Family Tree Guide to DNA Testing and Genetic Genealogy" by Blaine Bettinger. It's a bit out of date (there are five major companies now, not three) and has heavy overlap with the other book, but still a good resource. – Leah Worster Jun 26 '18 at 15:30

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