How do people get a color vision deficiency?
Most people are born with it (congenital). The most common forms of congenital defective color vision, the red-green deficiencies, are due to “sex-linked X chromosomes” and “simple recessive hereditary traits”. Men are mainly affected because women have two X chromosomes and men have only one X and a Y chromosome. If a man’s one X chromosome is color defective he will be color deficient, where as , a woman must inherit two color defective X chromosomes to be color deficient. For a woman to be color deficient, her father must be colorblind and her mother colorblind or be a carrier. All possible patterns of inheritance of any one of these color defects are shown here: A color-defective male always inherits his deficiency from his mother, who usually has normal color vision and is therefore a carrier of the defect. She may have received her color-deficiency gene from either her father (but only if he was color defective), or from her mother (who could have been a carrier herself, or rarel
