Solutions For An Introduction to Genetic Analysis Chapter 11 Problem 13P

The structural genes such as Z, Y, and A codes for proteins like β-galactosidase, lactose permease, and transacetylase respectively.

The repressor protein synthesized by gene ‘i’ binds to operator to inhibit transcription. If the bacterium is living in the absence of lactose and lactose is suddenly introduced into the bacterium's environment, then immediately the high concentration of lactose in the cell binds to the repressor and makes it unfit for binding. RNA (ribonucleic acid) polymerase can then transcribe the structural genes.

The lac Y gene synthesizes permease enzyme that transports lactose into the cell. The cell containing lacY mutation cannot transport lactose into the cell as a result the repressor continuously binds to the operator and thus β-galactosidase will not be induced.

In wild-type cells, the functional lacY gene transcription produces the protein permease that transports lactose into the cell, which binds to the repressor and induces the transcription of β-galactosidase even when the repressor is present. Thus, the permease allows lactose to enter the cell and initiate induction of the lac operon.

The table is as follows: