Where new genes come from A. Gene duplications 1. There are many, many kinds of mutations.
Transitions cause less disruption in the DNA helix during DNA synthesis.
With replacement substitutions, even a tiny change at the sequence level can have huge effects at the phenotypic level. This small change in the primary structure of hemoglobin has major effects for the action of hemoglobin. The sickle cell allele is not always completely deleterious. In the heterozygous state, in confers resistance to malaria, because the red cells infected with malaria are selectively destroyed. So roughly speaking, the sickle cell allele is beneficial in areas where malaria is common and deleterious in areas where malaria is uncommon.