With the exception of genes determining maleness, the Y chrom-osomes have no other genes. It affects males more frequently than females. A female who carries an abnormal gene on one of her X chromosomes is referred to as a carrier and in general has no or minimal symptoms. A female carrier has a 1 in 2 chance in every pregnancy with a male child of passing on the altered gene and thereby having a son with the con-dition. Examples of these conditions include Duchenne muscular dystrophy, hemophilia, and color blindness.
Genetic testing is available for many X-linked disorders.
Two of her four children are not affected. A son who inherited the genetic condition has died. The daughter who inherited the condition has two sons, both of whom have inherited the genetic condition. In disorders related to the 23 pairs of chromosomes, the defect is due to an error that occurs when either the egg or the sperm is forming and results in the fertilized egg having too many or too few chromosomes. This genetic imbalance is responsible for about half of all miscarriages or spontaneous abortions that occur in the first few weeks of pregnancy.