6. Which of the following is evidence for the single-cell origin of a tumor?a. All cells in one tumor express the same oncogenes.b. In a tumor from a female, some cells have one X chromosome inactivated and some have the other X chromosome inactivated.c. All cells in one tumor from a female have the same X chromosome inactivated.d. All cells in a tumor express both sex chromosomes, whether they be X or Y.
c. All cells in one tumor from a female have the same X chromosome inactivated.
a. All cells in one tumor express the same oncogenes is evidence for the single-cell origin of a tumor. This is because oncogenes, which are genes that can cause normal cells to become cancerous, are mutations that occur in a single cell. As the cell divides, it passes on this mutation to all of its daughter cells, leading to a tumor composed of cells with the same mutated oncogenes. This is referred to as clonal expansion, where all cells in the tumor originate from a single mutated cell. Therefore, option A is the correct answer.
Option B is not evidence for the single-cell origin of a tumor. This is just a normal phenomenon that occurs in females due to X-chromosome inactivation.
Option C might suggest a single cell origin of a tumor in females due to X-chromosome inactivation, but it is not conclusive as different tumors can have different X chromosomes inactivated.
Option D is also not evidence for the single-cell origin of a tumor. This is because not all cells in a tumor will necessarily express both sex chromosomes.