However, when two people who each carry a changed or mutated copy of the same gene for a recessive condition have children, there is a chance with each pregnancy for the child to inherit the two changed or mutated copies from each parent.
If a mother is a carrier for an X-linked recessive form of EDS, she may have affected or unaffected sons, or carrier or unaffected daughters, depending on the second sex chromosome inherited from the father.
Since galactosemia is a recessive genetic disease, it is usually first detected on a newborn screening test, as most people are not aware that they are carriers of a gene mutation causing the disease.
Unlike the other MPS conditions, MPS II is inherited in an X-linked recessive manner, which means that the gene causing the condition is located on the X chromosome, one of the two sex chromosomes.
The mother also has a 50 percent chance of passing the defective recessive gene to her daughters who will be carriers of the disorder (like their mother), but will not show symptoms of the disease.
As of 2004 the genes causing isolated PDA have not been identified, but it is known that PDA can be inherited through a family in an autosomal dominant pattern or an autosomal recessive pattern.
The exact pattern of genetic transmission was not known as of 2004, however; autosomal dominant, autosomal recessive, and sex-linked inheritance patterns have all been studied and rejected.
If one parent has been diagnosed with an autosomal dominant form of VWD or both parents are carriers for an autosomal recessive form of VWD, then prenatal testing should be considered.
It happened, however, that a recessive colour in one generation becomes the dominant in a succeeding one.
Then, in the scheme below, if A b and (A)N b are two brothers who both marry normal wives N, their children N(A) in the first case will be all normal in appearance but will be carrying albinism recessive; and in the second case some will be pure normal individuals N, and some will be like the children of the first brother, i.e.