Can females be homozygous for X-linked traits?
• If the trait is mild (like color deficiency) a rare marriage might occur between a colorblind male and heterozygous female (the odds of that are 8% x 8% or 0.64 of 1% of all marriages or matings). Of those rare parents, half the sons and half the daughters will be affected. In the US population that comes out to about 1 color blind female in 600 female births. • If you’re talking about serious conditions like Duchenne muscular dystrophy it is almost impossible because the disease usually kills before reproductive maturity so all fathers are carrying the normal allele on the X. It would be very rare (about 1 in a million) for conditions like hemophilia because only 1 male in 20,000 might have that disease and reach reproductive maturity and find a spouse (who then has only a 1 in 20,000 chance of being heterozygous unless she is a relative). • Note that the Y chromosome makes elimination of X-linked mutations much more rapid than for autosomes where they can repose in heterozygous for
