Human Heredity 11th Edition by Michael Cummings

Exercise 28

Hypothetical metabolic disease in which protein E is not produced. Lack of protein E causes intellectual disability in humans. Protein E's function is not known, but it is found in all cells of the body. Skin cells from eight individuals who cannot produce protein E were taken and grown in culture. The defect in each of the individuals is the result of a single recessive mutation. Each individual is homozygous for her or his mutation. The cells from one individual were grown with the cells from another individual in all possible combinations of the two. After a few weeks of growth, the mixed cultures were assayed for the presence of protein E. The results are given in the following table. A plus sign means that the two cell types produced protein E when grown together (but not separately); a minus sign means that the two cell types still could not produce protein E.
Draw the pathway leading to the production of protein E.