dna
16 Gregor Mendel and biological inheritance Charles Darwin1 , for all he contributed to the science of biology, never knew about the mechanism by which living things inherit traits from previous generations, or how new traits arise. As any schoolchild can tell you, this mechanism of interitance has since been found to be DNA2 , or deoxyribonucleic acid. DNA allows for stable inheritance of traits: the code in each strand of DNA is replicated precisely through the pairing of basic units along each strand. The error rate in this replication is amazingly low; not even one base pair in a million matches out of sequence. However, when even one base pair is added to a new strain of DNA in an order differently than in the parent chain, it can be the basis of a mutation. These changes in DNA sequences are the microscopic origin of changes in traits of all studied living things. Even the smallest difference in a strand of DNA can result in a change in traits that can cost the life of the organism. Mutations can produce proteins with a new or altered function. In humans, the example of Sickle cell anemia3 is commonly given as its origin is a difference of only one base pair in a section of DNA that encodes red blood cells. Individual sequences of DNA that encode for specific proteins are called genes and are the units of heredity. Each one has a set nucleotide4 , and together all of the genes and some sequence of DNA that apparently do not code for any biologically important functions together make up the entire chromosome5.