Summary PRINCIPLES OF GENETICS MODERN SCIENCE AND ARTS .

I INTRODUCTION Genetics is the scientific study of inherited variation. Human genetics is the scientific study of inherited human variation. This field has been energized in recent years by the Human Genome Project. Scientists expect that the project will lead to the development of new drugs targeted to specific genetic disorders. Increasingly, modern genetics involves genetic engineering; a technique used to manipulate genes and has produced many advances in medicine. II PRINCIPLES OF GENETICS • The site where genes work is the cell. • Each cell’s function within an organism is determined by the genetic information encoded in DNA. • In eukaryotes (organisms whose cells contain a nucleus), DNA resides within membrane-bound structures in the cell (nucleus, mitochondria, and chloroplasts in plants). • In prokaryotes (one-celled organisms that lack internal membranebound structures), DNA floats freely within the cell body. • DNA is packaged into structures called chromosomes within a cell. • Every chromosome in a cell contains many genes, and each gene is located at a particular site, or locus, on the chromosome. • Chromosomes usually occur in matched pairs called homologues. • The number of homologous chromosomes in the human body contain 23 pairs of chromosomes. Animal Cell • An animal cell typically contains several types of membranebound organs, or organelles. • The nucleus directs activities of the cell and carries genetic information from generation to generation. • The mitochondria generate energy for the cell. • Proteins are manufactured by ribosomes, which are bound to the rough endoplasmic reticulum or float free in the cytoplasm. • The Golgi apparatus modifies, packages, and distributes proteins. • Lysosomes store enzymes for digesting food. • The entire cell is wrapped in a lipid membrane that selectively permits materials to pass in and out of the cytoplasm. A. Cell Division and Reproduction • Organisms use two types of cell division to ensure that DNA is passed down from cell to cell during reproduction. • Simple one-celled organisms reproduce by a process called mitosis. During mitosis a cell doubles its DNA before dividing into two cells and distributing the DNA evenly to each resulting cell. • Organisms that reproduce sexually produce special cells called gametes, or egg and sperm. • During sexual reproduction, an egg and sperm unite to form a zygote, in which the full number of chromosomes is restored. The Human Life Cycle