Why is Colorblindness More Common in Males?

Observation during scientific research in 1911 determined women pass the gene for red-green (inability to see red or green) color blindness to sons. Females have two-gender specific X chromosomes, while males have one X and one male Y-chromosome. The color blindness defective gene attaches to one of the X chromosomes in the mother and with a male fetus, a fifty percent chance exists; the baby boy has the color blind allele (gene). The condition occurs when the defective X chromosome passes to the child instead of the normal X.

Single Gene Disorder

• Single gene disorders reflect on the X chromosome. Color blindness rides on one of the two X chromosomes a female has. Women rarely have color blindness due to the fact there are two X chromosomes (one is normal), while males have only one X.

How Girls Get Color Blind

• Passing two X chromosomes for color blindness to a female only happens when both the mother and father carry the red-green color blindness allele. When the two X chromosomes (one from dad and one from mom) knocks out the one normal X chromosome of the mother, and then the daughter is color blind.

Boys Never Get Dad's Color Blindess

• During conception when a male sperm carrying the Y chromosome enters the female egg, the fetus becomes a male baby. Though dad is color blind, the X chromosome he carries with the defect does not pass to the male fetus because the baby inherits only the duplicate Y chromosome.

Dad Gives the Gene to Daughters

• Because daughters receiving the defective X chromosome for color blindness from dad as "obligate carriers," every female child of a color-blind father has the gene. Obligate carriers have the disease-causing allele but rarely have the symptoms because they have the healthy working copy of the other X chromosome from their mothers.

Numbers

• Depending on how many offspring the female carrier has in her lifetime, fifty percent of the sons contact the disease and fifty percent of her daughters carry the diseased allele. All remaining children possess the normal copies of the X gene.