Beautiful boys Tyrelle and Tyreece Charles, from Cramlington, Northumberland, are twins, born six minutes apart - but they look very different. Now aged eight, the twins share the same cheeky grins but Tyreece is almost a foot taller than his twin, has darker skin and afro hair while his brother Tyrelle is blonde.
Their mum, Julia Charles, has white parents and their dad, Timothy Charles, has a black father and white mother.
The twins owe their different appearances to a one in a million combination of their parents' genes.
Julia, a full-time carer, said: 'When Tyreece popped out after Tyrelle the midwife and the nurses were utterly shocked. The doctor said he had never seen anything like it.
"We've been told it is very unusual, and people are always amazed when we tell them they are both twins.
"After they popped out, Tim just shouted to me, 'we've got one of each', and I couldn't believe it. Tyreece was so dark and Tyrelle was lily white.
Their dad Timothy said: "We were chuffed, shocked and so surprised when they came out. I was completely made up. It was hard getting them back off the nurses."
The couple, both 50, have been together since they were 12 years old and have five other children, Salina, 34, Tristan, 18, Shellee, 15, Julia, 13 and Clareena, 11.
Salina, Tristan and Clareena are dark skinned, while Shellee and Julia are paler.
The twins, their youngest children, were born in October 2005. Tyrelle was born first and weighed two pounds more than Tyreece. Now Tyreece is taller than Tyrelle and likes to take care of his brother. When they were younger, the boys' appearance was even more dramatically different with Tyrelle's blonde mop of curls and Tyreece dark haired.
Tyrelle told North News: "I'm white, I'm like me mam. I like watching Doctor Who but Tyreece doesn't like it, he likes playing football. I like tennis and he likes playing with his friends."
Their dad said: "Tyrelle has learning difficulties so Tyreece is very protective of him. Tyreece has been bullied in the past for the colour of his skin, but we tell him to just walk away.
"People have asked whether Tyrelle is my adopted son, they would say 'he can't be yours'. It is when they hear him shout 'Dad' and then people just ask and they find it unbelievable.
Skin colour is determined by combinations of genes. If a woman is mixed race, her eggs will usually contain a mix of gene coding for both black and white skin. The same goes for the sperm from a mixed race man. Very rarely, the egg or sperm might contain genes coding for one skin colour. If both the egg and sperm contain all white genes, the baby will be white. And if both contain just the versions necessary for black skin, the baby will be black.
For a mixed-race couple, the odds of either of these scenarios is around 100 to one. The rarity increases dramatically if the woman conceives non-identical twins with two eggs fertilised by two sperm - another 100 to one chance. If a sperm containing all white genes fuses with a similar egg, and a sperm coding for purely black skin fuses with a similar egg, two babies of dramatically different skin colours are born.
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