Figure 1.

Examples of gene effect complexity. (A). Dominant: a single mutated allele is enough to cause the disorder (B). Recessive: two mutated alleles are required to cause the disorder (C). X-linked: males that carries the disease-causing mutation are affected due to the single copy of the X chromosome (D). Penetrance: same genetic variant might not develop the same symptomatology in different individuals (E). Polygenic: disorder caused by the combined action of more than one gene (F). Pleiotropy: mutations in a single gene affects two or more apparently unrelated disorders.