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Genetics/Was it the milkman? Hair/eye color.


"So im watching Barbie and the 12 dancing princesses with the kiddos and I notice that the picture of the queen, she has medium brown hair and hazel eyes and the king has blonde hair and blue eyes, yet the oldest princess, their daughter, has black hair and brown eyes. Can anyone with basic biology skills say, milkmans baby?" As I hear it hazel eyes are not well understood. Is it possible for the king and queens child to come out with brown eyes and black hair. I know color can skip generations and it might depend on the grandparents and other multiple genes can determine the outcome.

Hi Anthony! Yeah, that sort of depiction makes you wonder.  Skin, eye, and hair color are very popular questions. Unfortunately human pigmentation is something we don't understand all that well yet genetically.

A general explanation. Genetics can be thought of as the 'cards' we're dealt at conception. What does this mean? When a lady makes egg cells, her body takes all her genes, shuffles them like cards, and then deals out one-half a deck to each cell. Guys do the same thing with sperm cells. When a baby is made, his and her 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 colors or four suits'. Really, human inheritance has many possible pictures for each card number. We call different pictures in each card position 'alleles'. The total combination of card values/alleles will affect the outward appearance of the children, who gets one allele 'picture' from each parent. If you look at my references at the bottom, hopefully this introduction will help those articles make more sense.

But what about skin/hair color? If we imagine a person as a factory, there is a whole department in the factory dedicated to producing the two known pigment genes, 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. What color we see at the end is a summation of the entire department's efforts, which could be ten or more genes. Also, the instructions on what to make can vary over time given how old the person is. Most often people's hair darkens at maturity, then grays at seniority, but this is not a hard and fast rule. Sometimes skin tone is darkest during youth but bleaches with old age.

Eyes. 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. Each child inherits three genes for eye color from each parent, and each gene is an on/off. it's 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 often half 'blue' allele and half 'brown' allele, and dark brown eyes have genetic alleles for loads of pigment.  Green or hazel eyes are rare because you need just the right amount of pigment from one parent, and usually none from the other. In this instance the blue eyed king is helpful.

So, princess A could have brown eyes and black hair, if she picked up a mutation that vastly increased the amount of hair and eye melanin produced. She'd be the only standout raven haired princess in the family, though, and it would be much more statistically likely to see if her features matched someone else at Court, or a previous royal marriage.

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