Tay-Sachs is fatal in early childhood. Sickle Cell Anemia Hemoglobin has a shape which can not pick up oxygen effectively and the rbcs fracture andblock blood flow. This can cause stroke or heart attack, as well as inhibit circulation ingeneral. The partial sickle effect of heterozygotes does not negatively affect health, and confers resistance to the malaria-causing protist. Cystic Fibrosis Excessive mucus production, especially in lungs and pancreas.
Breathing is affected, and individuals are very susceptible to infections.
Many individuals die in childhood. As mentioned, those dominant alleles that negatively impact individuals are rare in the population. The exceptions are dominant alleles that express themselves post-reproductively, such as Huntington's disease, which causes the brain to deteriorate a disease that affected Woody Guthrie. Although it is now possible to identify and screen for the Huntington's dominant allele, many who have the trait in their pedigree may choose not to go through the testing procedure. It is fairly easy to observe our 46 human chromosomes and their shapes, because we can obtain a karyotype, or chromosome display during the metaphase stage of cell division.