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Name: Fred W.
Status: Other
Age: Old
Location: N/A
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Date: N/A 

Because a Daughter receives the fathers alleles inherited from one of His Paternal Grandmother's, is She unrelated to the Paternal Grandfather?

Well... your words, "receives the fathers alleles inherited from one of His Paternal Grandmother's" Ieads me to think you are thinking the x and y chromosomes are the only chromosomes. In any case the granddaughter is definitely blood related since her father got 1/2 his genes from his father and 1/2 from his mother.

Peter Faletra Ph.D.
Office of Science
Department of Energy

remember that the sex chromosome is only one of the chromosomes that the son inherits. He will also inherit all of the other 22 chromosomes as well. So even though he may not have any of the genes on the grandfather's X, he has the possibility of inheriting other genes from the grandfather on the other chromosomes. So, yes, they are related genetically.


I will answer assuming you really do mean HIS (the father's paternal grandfather), and not HER (the daughter's) paternal grandfather. Starting with the oldest generation, the Paternal Grandfather and Grandmother had a son (Son A) that inherited (roughly) half of his alleles from each parent. Son A married and had Son B (the "Father" in your question). Son B inherits half of his alleles from each parent. So, Son B has one quarter of the paternal grandfather's alleles, and one quarter of the paternal grandmother's alleles, as well as one quarter each of the Maternal grandfather's and grandmother's alleles. Son B has a daughter, who inherits half of her DNA from each parent. So she has one eighth each of:

her dad's (=Son B) paternal grandfather's alleles,
her dad's (=Son B) paternal grandmother's alleles,
her dad's (=Son B) maternal grandfather's alleles,
her dad's (=Son B) maternal grandmother's alleles,
her mom's (=Son B's wife) paternal grandfather's alleles
her mom's (=Son B's wife) paternal grandmother's alleles
her mom's (=Son B's wife) maternal grandfather's alleles
her mom's (=Son B's wife) maternal grandmother's alleles

This is an idealized case due to simplifying a few technical details (i.e., ignoring recombination, the sex chromosomes, and the cytoplasmic inheritance of mitochondrial DNA for the purists), but addresses what I think is the thrust of your question.

Dear Fred:

In a very few words, you have introduced a lot of issues. What I suggest, is that you break the problem down into much simpler parts.

Genetic information is carried on chromosomes, of which there are 23 pairs in humans. When a new embryo is formed, one set of 23 chromosomes is inherited from the father, and one set of 23 chromosomes is inherited from the mother. (The X and Y chromosomes are kind of a special case, but let's just look at the general run of things here.)

So, the "Daughter" in your problem inherited one-half of all her genes from her father. That is a VERY close genetic relationship. A generation before, her father had inherited one-half of all of HIS genes from his father. So, the "Daughter", on average, inherited one-quarter of all her genes from her grandfather (the Father's father).

By the same line of reasoning, the Father's father inherited one-half of all HIS genes from his father, and so on. This means that the "Daughter" inherited one-eighth of all her genes from her Father's grandfather. That is a very close relationship, indeed. This means that the short answer to your original question would be "no."

Concerning your use of the expression "one of His Paternal Grandmother's," I suggest that you draw a family tree or pedigree, and work out why any given person only has ONE paternal grandmother. While I could describe this in words, your own picture will be a much better teacher.

For an excellent refresher on basic genetics, complete with problems to solve, historical notes, animations, and links to other genetics resources on the web, I suggest that you visit the Cold Spring Harbor Laboratory's "DNA From the Beginning: An Animated Primer on the Basics of DNA, Genes, and Heredity" which can be found at:

Tom Douglas

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