The DNA Connection DNA • Deoxyribonucleic acid • Genetic material that carries information about an organism and is passed from parent to offspring. • 1953: Watson and Crick figure out the structure of DNA (double helix). The Genetic Code • Genes control the production of proteins. • Proteins determine: – – – – Size Shape Color Many other traits of an organism Structure of DNA • Looks like a twisted ladder • Two sides of the ladder: – Made up of alternating molecules of deoxyribose and phosphates • Each rung is made up of a pair of molecules called nitrogen bases. Genes and DNA • DNA molecule – made up of 4 nitrogen bases • Adenine (A) and Thymine (T) • Guanine (G) and Cytosine (C) • (A) only pairs with (T) • (G) only pairs with (C) Mutations • Any change in a gene or chromosome • Mutation – Latin word that means “change” What happens when a mutation occurs? • Organism’s trait, or phenotype, may be different from what it normally would have been. Three Types of Mutations • Substitution – One base pair is substituted for another • Deletion – One base pair is removed • Addition – One base pair is added Effects of Mutations • A mutation is harmful if it reduces the organism’s chance for survival and reproduction. Example: white lemurs Effects of Mutations • Helpful mutations improve an organism’s chances for survival and reproduction. • Example: Antibiotic resistance in bacteria. Think about it! • We can use DNA fingerprinting to catch criminals. Should Americans be forced to give DNA samples so everyone is on file to make it easier to catch criminals?