false DNA is a DOUBLE HELIX molecule containing a specific sequence of NITROGENOUS BASES. Nitrogenous bases create a code for making PROTEINS. Chromosomes are strands of tightly wound DNA. Genes are secions of a chromosome that carry the code for a particular protein, which in turn affects the traits of an organism. PROTEINS Nitrogenous bases A, T, C, and G Proteins are used to build cells, tissues, organs, and to perform life processes. DNA provides the code that tells the cell exactly which proteins to make. The code is formed by the sequence of the bases A, T, C, and G along a section of DNA. SUGAR and PHOSPHATE molecules form the sides of the DNA molecule. Since these molecules are the same in all DNA, they are not written out as part of the code. PREEXISTING ORGANISMS MEIOSIS Sexual reproduction involves the production of sex cells through the process of MEIOSIS. Sex cells each carry half the parent's genetic material, and this produces variation between parents and offspring. Mitosis and Meiosis Mitosis results in two identical daughter cells Meiosis results in four daughter cells that are genetically different Mitosis - The result is two identical daughter cells. Meiosis - The result is four daughter cells (sex cells) which are not identical. 4 daughter cells (sex cells), each with 23 chromosomes (half the number of the parent cell). alleles Genotype is the genetic makeup, in this case, BB, Bb, or bb. Phenotype, based on genotype, is the appearance, in this case, purple or white. A Punnett Square Purple The genotype will be Bb in all four boxes. The chance of the offspring having the dominant trait is 100 percent. The phenotype will be purple in each box, so the possibility of a white offspring is 0 percent. A Punnett Square predicts the probability of the genotype and phenotype of the offspring. Those traits acquired through environmental influences cannot be inherited. adaptation Some organisms survive and reproduce, Some move out, Some die. A mutation is a change in the DNA sequence. Mutations can result from DNA copying mistakes made during cell division, exposure to radiation, exposure to certain chemicals, or infection by viruses. Only mutations in the sex cells of an organism will be inherited by offspring. Mutations in body cells are not passed on. Mutations can be good, providing an accidental advantage to an organism, helping its chance of survival (i.e. a mutation that gives a giraffe a longer neck allowing easy access to leaves). Mutations can be bad, providing a disadvantage to an organism and hurting its chance of survival (a mutation that gives a giraffe a shorter neck). Or a mutation can be neutral (a mutation that gives a giraffe a few extra spots). Giraffes with a tall mutation will be able to reach more food and have a better chance of surviving to have offspring and pass along this mutation. Over generations, more offspring will have the tall mutation. Those without the "tall" mutation are less likely to survive and produce offspring. This is natural selection. natural selection Adaptation makes an organism better able to survive in its environment. Genetic variation gives each dog a unique appearance. The fossil record documents the existence, diversity, extinction, and change of many life forms and their environments through Earth's history. The Theory of Evolution mutation, adaptation, natural selection, and extinction the fossil record, genetic information, and anatomical similarities across species. diversity The mice with the dark-color allele are best able to hide from predators and therefore the "fittest" for their environment. They are more likely to survive to reproduce, passing along the dark color gene to their offspring.