Autosomal dominant heredity: Dominant heredity exists if an allele (alternative forms of a gene) or a mutation has a discernible effect on the phenotype despite being heterozygous (its alleles differ). This means that a hereditary trait causes disease if two different alleles (one with defective, one with intact genetic material) exist in the homologous chromosome. Dominant traits always prevail. 

Autosomal recessive heredity: Recessive heredity exists if the effect of an allele or a mutation is not / is scarcely phenotypically discernible in the heterozygous state, yet phenotypical manifestation (disease) occurs in a homozygous state (a genotype’s alleles coincide). Thus, the disease is only caused if two identical alleles exist in the homologous chromosome, in other words the individual is homozygous with respect to this particular trait. A recessive trait only prevails if it occurs in a homozygous state.

X-linked recessive heredity: Man and women differ in their genetic material with respect to their so-called sex chromosomes. Women have two homologous X-chromosomes, whereas men have one X- and one Y-chromosome. Since mutations in the X-chromosome in men cannot be compensated for by another X-chromosome, they are particularly hard hit by the repercussions. Heterozygous women, on the other hand, are normally just conductors of the predisposition to disease. They pass on the trait to half of their sons, while half of their daughters become conductors themselves. A female conductor can pass the damaged X-chromosome on to her offspring without becoming ill herself. However, homozygous women will contract the illness and so will all their male offspring that inherit the defective gene from them. 

X-linked dominant heredity: Generally speaking, X-linked dominant inherited diseases are rare. Since their genetic information is in the X-chromosome, inheritance is sex-linked. If a man is affected, his sons - who only inherit his Y-chromosome - are trait-free; daughters, on the other hand, will certainly inherit the predisposition to disease. Overall, women are affected by an X-linked dominant disease much more frequently than men.