Genetics arose out of the identification of genes, the fundamental units responsible for heredity. Genetics may be defined as the study of genes at all levels, including the ways in which they act in the cell and the ways in which they are transmitted from parents to offspring. Modern genetics focuses on the chemical substance that genes are made of, called deoxyribonucleic acid, or DNA, and the ways in which it affects the chemical reactions that constitute the living processes within the cell. Gene action depends on interaction with the environment. DNA sequences in the nuclear diploid genome usually exist as two allelic copies (on paternal and maternal homologous chromosomes). In addition to this degree of repetition, about 40% of the human nuclear genome in both haploid and diploid cells is composed of sets of closely related nonallelic DNA sequences (DNA sequence families or repetitive DNA). Within the considerable variety of different repetitive DNA sequences are DNA sequence families whose individual members include functional genes (multigene families), and also many examples of nongenic repetitive DNA sequence families. This book is useful to researchers, molecular biologists, biotechnologists, plant breeders and teachers engaged in advanced genetics.