PCB Exposure as a Selective Pressure

Prior to the banning of polychlorinated biphenyls (PCBs) in the U.S., large quantities were routinely dumped into rivers as a means of disposal. For example, between the years 1947 and 1976, General Electric released over half a million kilograms of the chemical at plants upstream of the mouth of the Hudson River. The main concern over PCB exposure is its ability to cross the plasma membrane, bind to a cytoplasmic protein, and together translocate to the nucleus where the complex affects gene transcription.

Provide THREE observations that suggest that PCBs are perturbing a steroid hormone signaling mechanism.

Based on the similarities discussed above, predict what might happen to the tomcod population after prolonged exposure.

Analyze the data shown in the figure and provide a plausible explanation that is consistent with the data.

Pose an experiment and provide an outcome that would support the original finding.

Predict the resulting distribution of the AHR alleles in the Hudson River tomcod population if clean-up and regulations brought the PCB concentration down to negligible levels.