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Genetics/Two questions about genes?


Dear Trista Robichaud, PhD,
         I write to you today with two questions, both about inherited genes. First being that I have dark brown hair with natural red highlights all throughout my scalp and a red patches all across my beard. No one in my family (both immediate and extend) has red hair to my knowledge. So does this mean that I carry red hair gene along with the brown hair gene?
         Second question, my father has hazel-green eyes, and is the only one in his family. All my siblings and I have light brown eyes. I've heard from some sources that people with hazel eyes also carry the genes for blue and green eye's as well? If so, is it possible my siblings and I carry these genes?
         I apologize if these are silly questions, especially for someone of your caliber. Thank you for taking the time to read my questions.

Hey Alexander!  You've hit on two of three of my most popular questions; skin color, hair color, and the likelihood of green eyes.

First, some quick notes on how inheritance works. When you make egg cells, your body takes all your genes, shuffles them like cards, and then deals out one-half a deck to each egg cell. Guys do the same thing with sperm cells. When a baby is made, your and your significant other's DNA half-decks are combined to make a full deck of genes for each child. The number of cards (genes) is fixed. However, the pictures on the cards are not 'one of two' pictures. Really, human inheritance has many possible pictures for each card number. We call different pictures in each card position 'alleles'.

But what about hair or eye color?

Human pigmentation is something we don't understand all that well yet genetically. If we imagine a person as a factory, there is a whole department in the factory dedicated to producing the two known pigment genes for skin and hair, eumelanin (brownish) and pheomelanin (reddish). There are also support staff that indicate when the pigment is produced, how it is delivered, and where it goes, as well as how much the workers make. All of these factors are also controlled by DNA variations and genes. What color we see at the end is a summation of the entire department's efforts, which could be ten or more genes for skin and hair. It’s at least six for eyes. Also, the instructions on what to make varies over time given how old the person is. For example, most often people's hair darkens at maturity, then grays at seniority, but this is not a hard and fast rule. Personally, I started out with black hair as a newborn, then faded to honey-blonde like my mother, then darkened to a milk chocolate brown in my 30s. My father started out white-blond and then darkened to dark chocolate brown in his late 20s. My mother remains honey-blonde. You never know. :)

So yes, you and your relatives have a red hair gene. (pheomelanin) What is likely is that your genetic order form has your pigment factories make just as much red pigment as brown to give you those highlights. It appears in your case that as you age, the brown pigment washes out before the red does, so rather than having a salt and pepper beard you get red and brown. :)

There are six genes that pool together to make eye pigment; if you have very little pigment, you end up blue or gray. If you have lots, you get a dark brown eye. If a hazel-green eyed person has a blue-eyed spouse, the rule of thumb is you have a 50/50 chance that any child will have blue eyes or hazel-green eyes. This is because each child inherits three genes for eye color from each parent, and each gene is an on/off. Eye color is largely - but not always - governed by how much total pigment is made. Blue is least pigment, while green or hazel is an intermediate amount. Light brown is a medium amount of pigment, and dark brown is lots. Usually these pigment genes assort together; it takes some unlikely combinations to produce green eyes. If all your siblings have light brown eyes, it's likely that your mother had light brown eyes as well, and her genes mask your father's recessive hazel-green. You would have to find a blue-eyed spouse (completely recessive, pigment off) to reveal the possibility of blue or hazel-green eyed children.

There's a lot to read out there. Hopefully what I told you makes sense. Please feel free to come back if you have more questions.


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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)

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