Most sex-linked (X-linked) conditions are recessive. This means that person having two X-chromosomes (females), both copies of a gene (i.e., one on each X-chromosome), must have a change or mutation whereas in a person with one $\mathrm{X}$ - chromosomes (males), only one copy or a gene must have a mutation.
A female with a mutation in one copy of a gene on the Xchromosme is said to be a 'carrier' for an X-linked condition.
For X-linked recessive disorders, and unaffected carrier mother who has a mutation in a gene on the X-chromosome can transfer either the $\mathrm{X}$ - chromosome with this mutation or a normal X-chromosome to her children.
The pattern of inheritance of a condition directly or indirectly due to a dominant faulty gene located on autosome is known as autosomal dominant inheritance.
The condition caused directly or indirectly due to a recessive faulty gene copy on autosome is known as autosomal recessive inheritance.
Rare trait that is caused by single abnormal gene on the Xchromosome is called sex-linked dominant.