[{"data":1,"prerenderedAt":56},["ShallowReactive",2],{"tool:hairColor:en":3},{"faq":4,"sources":20,"html":33,"toc":34},[5,8,11,14,17],{"q":6,"a":7},"Can two dark-haired parents have a red-haired baby?","Yes, if both carry a hidden red version of the MC1R gene. Each of their children then has a 1 in 4 chance of red hair. Carriers look no different, which is why red hair in the family is the best clue.",{"q":9,"a":10},"Can two red-haired parents have a child without red hair?","In this model, no, because both parents have two red copies of MC1R and pass one on to every child. In real life the shade can still range from strawberry blond to deep auburn.",{"q":12,"a":13},"Does red hair skip a generation?","It can look that way. The red version of MC1R is recessive, so it can pass quietly through dark-haired or blond carriers and show up again in a grandchild.",{"q":15,"a":16},"My baby's hair does not match the result. Why?","Hair changes a lot in the first years. Newborn hair often falls out and grows back differently, and light hair commonly darkens through childhood and around puberty, so the colour at 6 months says little about the colour at 16.",{"q":18,"a":19},"Why are black and brown counted together?","The model uses one gene for dark versus light pigment, so it cannot tell black from the many shades of brown. Those depend on a large number of genes with small effects.",[21,24,27,30],{"label":22,"url":23},"MedlinePlus Genetics (US National Library of Medicine): Is hair color determined by genetics?","https:\u002F\u002Fmedlineplus.gov\u002Fgenetics\u002Funderstanding\u002Ftraits\u002Fhaircolor\u002F",{"label":25,"url":26},"Valverde P et al. Variants of the melanocyte-stimulating hormone receptor gene are associated with red hair and fair skin in humans. Nature Genetics 1995;11:328-330","https:\u002F\u002Fpubmed.ncbi.nlm.nih.gov\u002F7581459\u002F",{"label":28,"url":29},"The Tech Interactive, Ask a Geneticist: What are the chances my child will have red hair and blue eyes?","https:\u002F\u002Fwww.thetech.org\u002Fask-a-geneticist\u002Fask162",{"label":31,"url":32},"Morgan MD et al. Genome-wide study of hair colour in UK Biobank explains most of the SNP heritability. Nature Communications 2018;9:5271","https:\u002F\u002Fpmc.ncbi.nlm.nih.gov\u002Farticles\u002FPMC6288091\u002F","\u003Ch2 id=\"what-decides-hair-colour\">What decides hair colour\u003C\u002Fh2>\n\u003Cp>Hair colour comes from two pigments. \u003Cstrong>Eumelanin\u003C\u002Fstrong> is brown to black, and \u003Cstrong>pheomelanin\u003C\u002Fstrong> is red to yellow. Lots of eumelanin gives black or brown hair, and very little gives blond. When both copies of a gene called \u003Cstrong>MC1R\u003C\u002Fstrong> carry certain changes, the hair cells switch to making mostly pheomelanin, and the hair is almost always red.\u003C\u002Fp>\n\u003Cp>Many genes set the exact amounts, so real hair colour is a smooth range of shades. The calculator keeps the two effects that matter most for the question parents ask: dark or light, and red or not.\u003C\u002Fp>\n\u003Ch2 id=\"the-two-gene-model\">The two-gene model\u003C\u002Fh2>\n\u003Col>\n\u003Cli>\u003Cstrong>A pigment gene, dark or light.\u003C\u002Fstrong> Dark is dominant. Two dark copies, or one dark and one light, give black or brown hair. Two light copies give blond hair.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>MC1R, red or not red.\u003C\u002Fstrong> Red is recessive. Two red copies give red hair, whatever the pigment gene says. One red copy shows no red, but the parent can pass it on.\u003C\u002Fli>\n\u003C\u002Fol>\n\u003Cp>Each biological parent passes one copy of each gene to the child at random, and the calculator adds up every combination.\u003C\u002Fp>\n\u003Ch2 id=\"the-assumptions-about-hidden-genes\">The assumptions about hidden genes\u003C\u002Fh2>\n\u003Cp>You cannot see which hidden versions a parent carries, so the calculator uses stated, rough averages:\u003C\u002Fp>\n\u003Cul>\n\u003Cli>\u003Cstrong>Light pigment:\u003C\u002Fstrong> 4 in 10 pigment copies in the population are assumed to be light, which makes about 16% of people blond. A dark-haired parent then carries a hidden light copy 4 times in 7 and passes it on about 29% of the time. Blond is much rarer in southern Europe and more common in the north, so this is a middle value.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Red:\u003C\u002Fstrong> a parent without red hair is assumed to carry the red version 1 time in 3. That fits the UK, where 4.6% of adults have natural red hair (UK Biobank). If someone in their family has red hair, the calculator raises this to 1 in 2. It would be certain if the parent's own mother or father has red hair, and lower if it is a distant cousin.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>A red-haired parent:\u003C\u002Fstrong> red hides the pigment gene, so the calculator uses the population average for it.\u003C\u002Fli>\n\u003C\u002Ful>\n\u003Ch2 id=\"a-worked-example\">A worked example\u003C\u002Fh2>\n\u003Cp>A red-haired parent and a brown-haired parent with a red-haired sister: the red-haired parent always passes on red, and the brown-haired parent does so 1 time in 4 under the family assumption. So the child has a 25% chance of red hair.\u003C\u002Fp>\n\u003Cp>For the other 75%, blond needs a light pigment copy from both parents: 40% from the red-haired parent times about 29% from the brown-haired one, so about 11%. That gives about 9% blond and about 66% black or brown.\u003C\u002Fp>\n\u003Ch2 id=\"typical-results-without-red-hair-in-the-family\">Typical results without red hair in the family\u003C\u002Fh2>\n\u003Ctable>\n\u003Cthead>\n\u003Ctr>\n\u003Cth>Parents\u003C\u002Fth>\n\u003Cth>Black or brown\u003C\u002Fth>\n\u003Cth>Blond\u003C\u002Fth>\n\u003Cth>Red\u003C\u002Fth>\n\u003C\u002Ftr>\n\u003C\u002Fthead>\n\u003Ctbody>\u003Ctr>\n\u003Ctd>Dark and dark\u003C\u002Ftd>\n\u003Ctd>91%\u003C\u002Ftd>\n\u003Ctd>8%\u003C\u002Ftd>\n\u003Ctd>1%\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd>Dark and blond\u003C\u002Ftd>\n\u003Ctd>71%\u003C\u002Ftd>\n\u003Ctd>28%\u003C\u002Ftd>\n\u003Ctd>1%\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd>Blond and blond\u003C\u002Ftd>\n\u003Ctd>0%\u003C\u002Ftd>\n\u003Ctd>99%\u003C\u002Ftd>\n\u003Ctd>1%\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd>Red and dark\u003C\u002Ftd>\n\u003Ctd>80%\u003C\u002Ftd>\n\u003Ctd>10%\u003C\u002Ftd>\n\u003Ctd>10%\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd>Red and blond\u003C\u002Ftd>\n\u003Ctd>54%\u003C\u002Ftd>\n\u003Ctd>36%\u003C\u002Ftd>\n\u003Ctd>10%\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd>Red and red\u003C\u002Ftd>\n\u003Ctd>0%\u003C\u002Ftd>\n\u003Ctd>0%\u003C\u002Ftd>\n\u003Ctd>100%\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003C\u002Ftbody>\u003C\u002Ftable>\n\u003Ch2 id=\"hair-changes-as-children-grow\">Hair changes as children grow\u003C\u002Fh2>\n\u003Cp>The hair a baby is born with often falls out in the first months and grows back in a different shade. After that, light hair commonly darkens through childhood, and again around puberty, possibly because some pigment genes become more active with age. Plenty of blond toddlers become brown-haired adults, so the calculator describes the likely adult colour, not the colour in baby photos.\u003C\u002Fp>\n\u003Ch2 id=\"limits-of-the-model\">Limits of the model\u003C\u002Fh2>\n\u003Cp>This is a simplified model, and real inheritance is more complex. Dozens of genes nudge the amount of each pigment, so two blond parents can have a brown-haired child, and black and brown cannot be told apart here. The carrier figures are averages, not facts about your family. Grey and white hair, which come with age, are not part of it. Treat the percentages as a fun estimate, not a genetic test.\u003C\u002Fp>\n",[35,38,41,44,47,50,53],{"id":36,"text":37},"what-decides-hair-colour","What decides hair colour",{"id":39,"text":40},"the-two-gene-model","The two-gene model",{"id":42,"text":43},"the-assumptions-about-hidden-genes","The assumptions about hidden genes",{"id":45,"text":46},"a-worked-example","A worked example",{"id":48,"text":49},"typical-results-without-red-hair-in-the-family","Typical results without red hair in the family",{"id":51,"text":52},"hair-changes-as-children-grow","Hair changes as children grow",{"id":54,"text":55},"limits-of-the-model","Limits of the model",1793362217902]