A researcher prepares three cell cultures in a medium containing an equal mixture of glucose and lactose. Culture 1 contains E. coli cells lacking the lac operon. Culture 2 contains E. coli cells with the lac operon, and Culture 3 contains E. coli cells modified such that the lac operon always allows the metabolism of lactose. All cultures are left for 24 hours in appropriate conditions. Rank the cultures in order of increasing numbers of cells.

Culture 2 is expected to contain most cells because the lac operon metabolizes lactose only when the cells are needed and saves energy for replication. However, since cells in culture 3 can metabolize lactose, we can expect slightly fewer cells in culture 3, but they are not very efficient in terms of energy. Culture 1 dramatically reduces the number of cells because these cells cannot metabolize lactose.

The gene is the basic physical and functional unit of heredity. Genes are made up of DNA. Some genes act as instructions for making molecules called proteins. However, many genes do not encode proteins.

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