This document discusses various genetics concepts including selective breeding, inbreeding, hybrids, test crosses, genetic engineering, and cloning. Selective breeding involves mating organisms with desired traits to produce offspring with those traits, and has been used to develop breeds of dogs, farm animals, and crop varieties. Inbreeding can increase undesirable recessive traits by making offspring homozygous. A hybrid is heterozygous with different forms of a trait from its parents. A test cross determines an unknown genotype. Genetic engineering uses restriction enzymes and vectors to insert recombinant DNA from one organism into another, creating transgenic organisms. Cloning produces genetically identical copies through nuclear transfer.