http://www.mirror.co.uk/news/ampp3d/how-white-baby-can-born-4145688How a white baby can be born to a black mother - the statistics of skin colour
Sep 01, 2014 17:52 By Sophie Warnes
This week, new parents Catherine and Richard were shocked to find their baby boy has totally Caucasian skin, and not a darker tone as expected. It was a one in a million chance - but here's how it happens.
Catherine Howarth with baby Jonah and husband Richard
Catherine and Richard Howarth were convinced they'd been given the wrong child by mistake - their newborn baby boy was white and not dark-skinned as they'd expected. It's an unusual story - but it's not the first time that it's happened. How does this sort of thing occur and why?
His mother probably had a white ancestor
The baby's father Richard is white, but mum Catherine has dark skin from her Nigerian heritage. Genes from one of her ancestors may have lain dormant for generations - until randomly thrown together in the new baby, they brought out traits that had been latent for so long. This is what's known as a genetic/evolutionary throwback, or atavism.
A one in a million chance
Melanin is the pigmentation in skin that determines a person's skin colour. Groups of people whose ancestors lived closer to the equator - where there's more UV radiation - tend to have darker skin.
But the combinations of genes thrown up everytime a baby is born means that mixed-race child can be anywhere on a spectrum between its two parents.
The genes that control the amount of melanin in someone's skin operate under "incomplete dominance" which means no specific trait over-rules the others. All of the variant gene traits are completely expressed, and visually this will mean a mixed-race child's skintone will be a visual mix of its parents.
This chart shows how that works with two parents with three white-skin alleles (gene traits), and three black-skin alleles. The use of six gene traits is just an example to show how the mixing can produce many different combinations.
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You can see that the chance of a baby with Caucasian skin tone is 1/64 for parents with three dark-skin alleles each. However, the chances would be far lower for this to happen in Catherine's case, as the recessive gene could be just one in 20 alleles - in fact, the chances of this happening were calculated at roughly one in a million!
But those one in a million chances happen. It's the nature of statistics that statistically unlikely events still happen every so often. So it may be surprising, but it's not out of the normal.
The chart also shows that few people are 100% white-skinned or 100% dark-skinned. The vast majority of people fall on the spectrum in between. But though geneticists understand skin colour that way - it's not how society views skin colour. Socially we tend to put people in much simpler categories: black or white or brown. That means we find it hard to understand natural genetic variation. Throughout history it has been used to justify wars and inequality.
Born to racist parents in South Africa
The story of a baby coming out a surprising colour isn't the first of its kind - there have been many examples of children being born a different colour to their parents.
One of the saddest - and most famous - stories is that of Sandra Laing. Sandra is a black-skinned woman who was born to white parents in apartheid South Africa and forced to leave home at the age of ten.
People have also had children who have differently-coloured skin to their siblings. In 2005, Kylee Hodgson and Remi Horder had twin girls - one black and one white.
If you're really fascinated by learning about genetic variations in skin colour, we recommend this really great Wikipedia article which goes into a lot of depth on the subject.
