You are here:

Genetics/genetic genealogy help


I have a family mystery to solve, but I'm really having trouble wrapping my head around it- either someone is not telling the truth, or DNA percentage was misread. I'm hoping you could help me sort this mess out a bit.

In a nutshell...

Root person: joe
Joe was given up for adoption by Jane.

Jane has a sister,Patrice, who had a baby and gave him up for adoption around the same time as when joe was born.

Jane & Patrice's mother's name is Marie.

Marie has a sister named Jamie.

Jamie adopted a son and named him David.

Joe claims that he has a 12.5% DNA match to Jamie.

Joe also claims to have a 12.5% DNA match to David.

Obviously this should be imlikely, since David was adopted, but it is suspected that David is actually Patrice's son that she gave up for adoption.

I'd it possible that Joe could have the same 12.5% DNA match with his cousin & great aunt?

If you could help me sort this out, even a little bit, if be very grateful.

Thanks for your time!

Please forgive the lateness of my reply. I needed to find some time to sit down and work this out.

In my understanding, if Patrice gave birth to David, then Joe and David would be cousins. It is reasonable to say that Joe and David would have about 12.5% of their DNA in common. Each time you hop on the family tree, you multiply by 1/2. So you to your Mom would be 1/2, you to Grandma would be 1/4, you to an aunt would be 1/4, and so on.

Joe probably looked at this site:

It has a great explanation at the bottom of the page.

Now, Great-Aunt Jaimie is also three steps away from Joe on the family tree.

Which means that Joe has 12.5% DNA in common with Jaimie. No lying, but rather weird nonetheless.

It's worth noting that the 12.5% Joe shares with Jaimie is probably not the same 12.5% he shares with David, if David is indeed his cousin. :) If David were a blood son of Jaimie, then Joe would only share 6.25% of his DNA with him.

However, none of this should get Joe out of doing the dishes. :)


All Answers

Answers by Expert:

Ask Experts


Trista Robichaud, PhD


No homework questions, especially ones copied and pasted from textbooks. I will answer questions about principles or give hints, but I do not do other's homework. I'm comfortable answering basic biochemistry, chemistry, genetics, and biology questions up to and including an undergraduate level of understanding. This includes molecular biology, protein purification, and genetics. My training/inclination is primarily in structural biology, or how the shapes of things affect their function. Other interests include protein design, protein engineering, enzyme kinetics, and metabolic diseases such as cancer, atherosclerosis, and diabetes. Regrettably, I cannot diagnose any disease. I can tell you how we currently understand the basic science behind a disease state, but I cannot recommend treatment in any way. Please direct such questions to your medical professional.


I hold a PhD in Biomedical Science from the University of Massachusetts Medical School in Worcester. I specialize in Biochemistry, with a focus on protein chemistry. My thesis work involved the structure and functions of the human glucose transporter 1. (hGLUT1) Currently I am a postdoc working in peptide (mini-protein) design and enzymology at the University of Texas Health Science Center in San Antonio, Texas. I am in Bjorn Steffensen's lab, researching inhibitors of gelatinase A, a matrix metalloproteinase. I have also been answering Chemistry/Biochemistry questions on this site since summer 2010.

2001 American Association for the Advancement of Science, 2007 American Chemical Society 2007 Protein Society 2011 UTHSCSA Women’s Faculty Association

Publications Levine KB, Robichaud TK, Hamill S, Sultzman LA, Carruthers A. Properties of the human erythrocyte glucose transport protein are determined by cellular context. Biochemistry 44(15):5606-16, 2005. (PMID 15823019) Robichaud TK, Appleyard AN, Herbert RB, Henderson PJ, Carruthers A “Determinants of ligand binding affinity and cooperativity at the GLUT1 endofacial site” Biochemistry 50(15):3137-48, 2011. (PMID 21384913) Xu X, Mikhailova M, Chen Z, Pal S, Robichaud TK, Lafer EM, Baber S, Steffensen B. “Peptide from the C-terminal domain of tissue inhibitor of matrix metalloproteinases-2 (TIMP-2) inhibits membrane activation of matrix metalloproteinase-2 (MMP-2)” Matrix Biol. 2011 Sep;30(7-8):404-12. (PMID: 21839835) Robichaud TK, Steffensen B, Fields GB. Exosite interactions impact matrix metalloproteinase collagen specificities. J Biol Chem. 2011 Oct 28;286(43):37535-42 (PMID: 21896477) Poster Abstracts: Robichaud TK, Carruthers. A Mutagenesis of the Human type 1 glucose transporter exit site: A functional study. ACS 234th Meeting, Boston MA. Division of Biological Chemistry, 2007 Robichaud TK, Bhowmick M, Tokmina-Roszyk D, Fields GB “Synthesis and Analysis of MT1-MMP Peptide Inhibitors” Biological Chemistry Division of the Protein Society Meeting, San Diego CA 2010 Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon Research Conference on Matrix Metalloproteinase Biology, Bristol RI 2011

INSTITUTION AND LOCATION DEGREE (if applicable) YEAR(s) FIELD OF STUDY Oakland University, Auburn Hills MI BS 1993-1998 Biochemistry University of Massachusetts Medical School, Worcester MA PhD 2001-2008 Biochemistry & Molecular Pharmacology University of Texas Health Science Center, San Antonio TX Postdoc 2009-Present Biochemistry

Awards and Honors
1998 Honors College Graduate, Oakland University 2009 Institutional National Research Service Award, Pathobiology of Occlusive Vascular Disease T32 HL07446 2011 1st Place, Best Postdoctoral Poster, Dental Science Symposium, UTHSCSA, April 2011

Past/Present Clients
Invited Seminars: Robichaud TK, Fields GB. “Synthesis and Analysis of MTI-MMP Triple Helical Peptide Inhibitors” Pathology Research Conference, University of Texas Health Science Center San Antonio Pathology Department (June 18th, 2010) Robichaud TK & Hill, B “How To Give A Great Scientific Talk” Invited Lecture, Pathobiology of Occlusive Vascular Disease Seminars, UTHSCSA (Nov 11th 2010), Cardiology Seminar Series, Texas Research Park (Feb 21st, 2011) Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon-Keenan Research Seminar “Everything You Wanted to Know About Matrix Metalloproteinases But Were Afraid to Ask” Bristol, RI (Aug 6th, 2011)

©2016 All rights reserved.