This is, provided that spontaneous mutations do not take place. Single-celled organisms such as bacteria and yeast usually reproduce asexually. A clone may also be defined as A a replica of a DNA sequence, such as a gene, produced by genetic engineering. Genetic engineering entails eliminating or introducing specific genes into the nucleus. Plasmids found in certain kinds of bacteria and yeast can be used to transfer a gene by this process.
Plasmids are circular pieces of DNA that exist separately from the main chromosomes.
They contain very few genes and only those plasmids that confer some selective advantage will be maintained in a population. One advantage, antibiotic resistance, is beneficial when a bacterium has to compete against another microorganism that secretes antibiotics. By cloning such a plasmid many identical copies will be produced. A functional lacZ gene will produce the protein b - galactosidase. A mutant that has a nonfunctional lacZ gene will form white colonies.