[{"data":1,"prerenderedAt":58},["ShallowReactive",2],{"tool:eyeColor:en":3},{"faq":4,"sources":20,"html":35,"toc":36},[5,8,11,14,17],{"q":6,"a":7},"Can two blue-eyed parents have a brown-eyed baby?","In the simple two-gene model, no. In real life it is rare but possible, because many more genes than these two affect eye colour.",{"q":9,"a":10},"Can two brown-eyed parents have a blue-eyed baby?","Yes, if both carry a hidden blue version of the brown gene. In this model, with both parents carrying it, the chance is 6.25% for blue eyes and 18.75% for green.",{"q":12,"a":13},"When do babies get their final eye colour?","Many babies are born with blue or grey eyes that darken as the iris builds up pigment. Most have their lasting colour by about their first birthday, though small changes can continue until about age 3.",{"q":15,"a":16},"Why are hazel and grey grouped with green and blue?","The two-gene model only knows three colours. Hazel sits between green and brown, and grey behaves like blue, so each is counted with the nearest colour.",{"q":18,"a":19},"How reliable is this eye colour calculator?","It is a rough, fun estimate. It assumes both parents carry hidden versions of both genes, which is not always true, and real eye colour depends on at least ten genes.",[21,24,27,29,32],{"label":22,"url":23},"MedlinePlus Genetics (US National Library of Medicine): Is eye color determined by genetics?","https:\u002F\u002Fmedlineplus.gov\u002Fgenetics\u002Funderstanding\u002Ftraits\u002Feyecolor\u002F",{"label":25,"url":26},"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":28},"Eiberg H, Mohr J. Major genes of eye color and hair color linked to LU and SE. Clinical Genetics 1987;31(3):186-191",{"label":30,"url":31},"American Academy of Ophthalmology: 20 Things to Know About Children's Eyes and Vision","https:\u002F\u002Fwww.aao.org\u002Feye-health\u002Ftips-prevention\u002Ftips-children-eyes-vision",{"label":33,"url":34},"Jabbehdari S et al. Colour change in the newborn iris: 2-year follow-up of the Newborn Eye Screening Test study. Acta Ophthalmologica 2019","https:\u002F\u002Fpubmed.ncbi.nlm.nih.gov\u002F31811709\u002F","\u003Ch2 id=\"where-eye-colour-comes-from\">Where eye colour comes from\u003C\u002Fh2>\n\u003Cp>The colour of the iris depends mostly on how much melanin, a brown pigment, it holds. Lots of melanin gives brown eyes, a medium amount gives green or hazel, and very little gives blue. Blue eyes contain no blue pigment at all: they look blue for the same reason the sky does, because of how light scatters.\u003C\u002Fp>\n\u003Cp>How much melanin the iris makes is set by genes inherited from both biological parents. The biggest effect comes from a region on chromosome 15 that holds two genes, OCA2 and HERC2. Several other genes add smaller effects.\u003C\u002Fp>\n\u003Ch2 id=\"the-two-gene-model\">The two-gene model\u003C\u002Fh2>\n\u003Cp>Long before those genes were found, Danish researchers studying hundreds of families described eye colour with two genes, and this model is still the simplest way to explain it:\u003C\u002Fp>\n\u003Cul>\n\u003Cli>\u003Cstrong>bey2\u003C\u002Fstrong> (chromosome 15, today linked to OCA2 and HERC2) comes in a brown and a blue version. Brown is dominant.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>gey\u003C\u002Fstrong> (chromosome 19) comes in a green and a blue version. Green is dominant over blue, but a brown bey2 hides it.\u003C\u002Fli>\n\u003C\u002Ful>\n\u003Cp>Everyone has two copies of each gene. Any brown copy gives brown eyes. With no brown copy, any green copy gives green or hazel eyes. Only blue on all four copies gives blue or grey eyes.\u003C\u002Fp>\n\u003Ch2 id=\"the-assumption-about-hidden-genes\">The assumption about hidden genes\u003C\u002Fh2>\n\u003Cp>You cannot see whether a brown-eyed parent carries a blue version underneath. The calculator assumes each parent carries one copy of every hidden version their eye colour allows:\u003C\u002Fp>\n\u003Cul>\n\u003Cli>\u003Cstrong>Brown eyes:\u003C\u002Fstrong> one brown and one blue bey2, one green and one blue gey.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Green eyes:\u003C\u002Fstrong> two blue bey2, one green and one blue gey.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Blue eyes:\u003C\u002Fstrong> blue on all four copies.\u003C\u002Fli>\n\u003C\u002Ful>\n\u003Cp>This is the assumption behind the figures most often quoted for eye colour, such as 75% brown for two brown-eyed parents. If a brown-eyed parent really has two brown copies, all their children will have brown eyes, so for some families the chance of lighter eyes is lower than shown.\u003C\u002Fp>\n\u003Ch2 id=\"every-combination-at-a-glance\">Every combination at a glance\u003C\u002Fh2>\n\u003Ctable>\n\u003Cthead>\n\u003Ctr>\n\u003Cth>Parents\u003C\u002Fth>\n\u003Cth>Brown\u003C\u002Fth>\n\u003Cth>Green or hazel\u003C\u002Fth>\n\u003Cth>Blue or grey\u003C\u002Fth>\n\u003C\u002Ftr>\n\u003C\u002Fthead>\n\u003Ctbody>\u003Ctr>\n\u003Ctd>Brown and brown\u003C\u002Ftd>\n\u003Ctd>75%\u003C\u002Ftd>\n\u003Ctd>18.75%\u003C\u002Ftd>\n\u003Ctd>6.25%\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd>Brown and green\u003C\u002Ftd>\n\u003Ctd>50%\u003C\u002Ftd>\n\u003Ctd>37.5%\u003C\u002Ftd>\n\u003Ctd>12.5%\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd>Brown and blue\u003C\u002Ftd>\n\u003Ctd>50%\u003C\u002Ftd>\n\u003Ctd>25%\u003C\u002Ftd>\n\u003Ctd>25%\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd>Green and green\u003C\u002Ftd>\n\u003Ctd>0%\u003C\u002Ftd>\n\u003Ctd>75%\u003C\u002Ftd>\n\u003Ctd>25%\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd>Green and blue\u003C\u002Ftd>\n\u003Ctd>0%\u003C\u002Ftd>\n\u003Ctd>50%\u003C\u002Ftd>\n\u003Ctd>50%\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd>Blue and blue\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=\"a-worked-example\">A worked example\u003C\u002Fh2>\n\u003Cp>Take a brown-eyed parent and a blue-eyed parent. For bey2, the brown-eyed parent passes on brown or blue, half and half, and the blue-eyed parent can only pass on blue. So half of their children get a brown copy and have brown eyes.\u003C\u002Fp>\n\u003Cp>The other half have two blue bey2 copies, and gey decides. The brown-eyed parent passes on green or blue, half and half, and the blue-eyed parent passes on blue. So a quarter of all children have green eyes and a quarter have blue eyes. The result: 50% brown, 25% green, 25% blue.\u003C\u002Fp>\n\u003Ch2 id=\"why-your-baby-s-eyes-may-still-change\">Why your baby's eyes may still change\u003C\u002Fh2>\n\u003Cp>Many babies, especially those with light skin, are born with blue or grey eyes. The iris keeps adding melanin during the first months, so eyes often darken to green, hazel or brown. Babies born with brown eyes almost always keep them: in a US study that followed babies to age 2, 73 of the 77 born with brown eyes still had brown eyes. Most children have their lasting eye colour by about their first birthday, and small shifts can continue until about age 3.\u003C\u002Fp>\n\u003Ch2 id=\"limits-of-the-model\">Limits of the model\u003C\u002Fh2>\n\u003Cp>The model is simplified: real inheritance is more complex. MedlinePlus Genetics lists OCA2 and HERC2 plus eight other genes that shape eye colour, and their combined effect is more like a dimmer than an on and off switch. That is why two blue-eyed parents occasionally have a brown-eyed child, something the two-gene model calls impossible. Take the percentages as a fun guide to what is likely, not a prediction for your baby.\u003C\u002Fp>\n",[37,40,43,46,49,52,55],{"id":38,"text":39},"where-eye-colour-comes-from","Where eye colour comes from",{"id":41,"text":42},"the-two-gene-model","The two-gene model",{"id":44,"text":45},"the-assumption-about-hidden-genes","The assumption about hidden genes",{"id":47,"text":48},"every-combination-at-a-glance","Every combination at a glance",{"id":50,"text":51},"a-worked-example","A worked example",{"id":53,"text":54},"why-your-baby-s-eyes-may-still-change","Why your baby's eyes may still change",{"id":56,"text":57},"limits-of-the-model","Limits of the model",1793362217903]