, both haemophilia and colour blindness are X-linked recessive traits , . The female is a carrier with the defective genes on one X chromosome (genotype ) and the male is normal (). The sons receive their single X chromosome from the mother. Therefore, there is a 50% probability that a son receives the affected X chromosome (, diseased) and a 50% probability he receives the normal X chromosome (, normal) . All daughters will receive a normal X chromosome from the father and will be phenotypically normal (though 50% will be carriers).