SEX-LINKED RECESSIVE  (Hemophilia A, for instance, is a sex-linked recessive defect.)  1. On the average half the male offspring of a carrier dam are affected.  2. On the average half the female offspring of a carrier dam are carriers.  3. The trait may skip generations.  4. The pattern of transmission is often called oblique, because the gene goes from phenotypically normal dams, to affected sons, and then to phenotypically normal carrier daughters.  5. Affected males transmit the gene to all of their daughters and to none of their sons, because the sons receive the Y- and not the X-chromosome.  6. If both parents are affected with the trait, all offspring are affected.  7. For an affected female offspring to emerge, the dam must be at least a carrier, and the sire must be affected with the trait.  8. Most affected offspring in a typical pedigree are male.  9. There may be related affected males on the maternal side of the pedigree, but only rarely (if ever) on the paternal side.  10. All male offspring of an affected female are affected with the trait when the sire is normal, and all daughters are phenotypically normal carriers. 

AUTOSOMAL DOMINANT  Some forms of epilepsy and deafness are autosomal dominant.  1. At least one parent of an affected offspring must show the trait.  2. The trait occurs in successive generations (no skipping).  3. Males and females are affected equally.  4. About 50% of the offspring of an affected parent will be affected.  Autosomal Recessive PRA and brindle, for instance, are autosomal recessive traits. 1. Both parents are proven carriers, but generally show no phenotypic manifestation of the trait. 2. The trait tends to occur in one generation and then skips one or two generations until carrier descendants are again mated, allowing the genes to be expressed. 3. Males and females are affected equally. 4. Matings between carriers (heterozygotes) on the average produce 25% affected (homozygous recessive), 50% carriers (heterozygous) and 25% that do not have the mutant gene (homozygous dominant).