bacillus bacteria bacteriology biochemist chromosome clone(n) clone(v) cross crossbreed(v) crossbreed(n) cross-fertilize culture cytology DNA dominant double helix gamete gene genetic genetically modified genetic code genetic engineering genetics genome genotype germ hereditary heredity hybrid identical twin incubate inheritance insecticide microbe MRSA mutant mutate mutation nucleic acid parthenogenesis pasteurized pathogen pesticide plasma protozoan ptomaine recessive RNA salmonella superbug toxin transgenic virus weedkiller X chromosome Y chromosome zygote