Autosomal dominant disorders require only one mutation for the disease to be expressed.  Since an affected parent has two chromosomes, only one of which has the mutant gene, parents can expect that half (50%) of their children will receive that one and inherit the disease.  It is common for individuals that inherit the mutation, however, to not have evidence of the disease (nonpenetrance).

In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent.  Carriers with only one mutation, such as the parents, do not have clinical disease.  Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.

X-linked inheritance patterns result when disease-causing mutations are located on the X chromosome.  Males have one X chromosome while females have two.  A mutation on the male's X chromosome frequently is lethal or renders him unable to reproduce.  However, in rare cases when males have children, they can expect that all of then will inherit the condition. 

X-linked inheritance patterns result from mutations located on the X chromosome.  Females have two X chromosomes of which only one carries a mutation in X-linked dominant disorders.  This usually results in expression of the disease and women with a single mutation have the disorder caused by the mutation.  Half of their offspring, male and female, will inherit the mutation.  Men, with only one X chromosome, will always have the condition if they inherit the one with the mutation. Men would transmit it to all of their offspring.  Without a modifying normal gene on a second X chromosome, X-linked dominant conditions are frequently lethal in such males. The result is a vertical transmission pattern, usually from female to female.

X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children.  If the mutation is in a recessive gene and carried by the father, he has the disease since his only X chromosome is mutant and he has no normal X to blunt the effects of the abnormal gene.  His sons only receive his Y chromosome and thus are all normal.  However, all his daughters receive his one and only X chromosome and will be healthy 'carriers'.  Thus such males will have no affected children but half their grandsons from those daughters will have the same disease as he does.

X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children.  If the mutation is in a recessive gene and carried by the mother, she usually does not have the disease since the normal X chromosome without the mutation neutralizes the mutation in the abnormal X chromosome.  However, half her sons will inherit the mutation-containing X chromosome and therefore have the X-linked disease.  Half the daughters will inherit the mutation-bearing X chromosome and are usuallly healthy 'carriers'.