Ey up lads, it's time for a science lesson.
There's a new BBC2 series out called Countdown to Life. It explores how we develop in the womb and how early changes impact us as we grow older. As part of the show, the crew explore an extraordinary intersex condition, known medically as '5-alpha-reductase deficiency'.
Although when children, referred to as 'Guevedoces', are born in an isolated village in the Dominican Republic, they appear to be female. But when they reach puberty, things start to change.
'Guevedoces' literally translates as 'penis at 12', and at that age the children develop muscles, their chests start to grow, and by the age of 12, they sprout testes and a penis.
In the BBC show they meet Johnny, once known as Felicita, who suffers from the condition. He explains that during his childhood he was brought up as a girl called Felecitia by his parents.
Catherine and his cousin Carla, Guevedoces, in the Dominican Republic, another boy who sprouted a penis during puberty. Image credit: BBC.
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However, he says: "I never liked to dress as a girl and when they bought me toys for girls I never bothered playing with them - when I saw a group of boys I would stop to play ball with them."
The BBC reports that when he became obviously male he was bullied at school, and responded with his fists.
Johnny adds: "They used to say I was a devil, nasty things, bad words and I had no choice but to fight them because they were crossing the line."
He is one of many children who live in the village of Salinas, in the south of Dominican Republic, with the condition. It is believed that as many as one in 90 boys in the area are raised as girls, only to later develop external testes and a penis.
Dr Julianne Imperato brought '5-alpha-reductase deficiency' to general attention in the 1970s and found that while those with the condition are genetically male, they lack the enzyme - 5-alpha reductase - that converts testosterone to dihydro-testosterone, meaning that the boys are born looking like females.
However, at puberty their body is flooded with a surge of testosterone, and the body responds with the penis and testes developing.
The lack of this enzyme is genetic, with the condition abnormally prevalent in this particular region of the Dominican Republic.
Watch Countdown to Life: The Extraordinary Making of You, Against the Odds, on the iPlayer..
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Featured image credit: IFL Science
Featured Image Credit:Topics: BBC, Documentary