Analysis of the Abnormal White Blood Cells of a Patient

Analysis of the abnormal white blood cells of a patient with leukemia, a type of cancer, reveals that a protein, termed LP, is always functionally active.In normal white blood cells this protein is found to be only functionally active in response to growth stimuli that induce cell division.Surprisingly, sequencing of leukemic cell DNA shows that both LP alleles in the patient's leukemic cells are normal.However, the DNA sequencing also reveals that both alleles of protein ILP, which normally inhibits LP activity in the absence of growth stimuli, have each acquired a mutation.Further research proves that these _______ mutations in both ILP alleles are the reason why LP is always active and, consequently, induces the leukemic cells to constantly undergo cell division.

A) loss-of-function
B) gain-of-function
C) silent
D) reversion
E) conditional