Duchenne muscular dystrophy - normal female, chromosomes have been highlighted by a fluorescent probe for exon 45/47 (note the double yellow band). This disorder is caused by a recessive gene on the X chromosome, so is normally shown only by males, who lack a second X chromosome. The condition starts with difficulty in walking and climbing stairs in early childhood, usually resulting in confinement to a wheelchair by the age of 10, with death from respiratory infection or cardiac failure by about the age of 20.

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Credit: Duchenne muscular dystrophy - normal female, chromosomes have been highlighted by a fluorescent probe for exon 45/47 (note the double yellow band). This disorder is caused by a recessive gene on the X chromosome, so is normally shown only by males, who lack a second X chromosome. The condition starts with difficulty in walking and climbing stairs in early childhood, usually resulting in confinement to a wheelchair by the age of 10, with death from respiratory infection or cardiac failure by about the age of 20. Wessex Reg. Genetics Centre. Source: Wellcome Collection.