Question

stem cells are undifferentiated cells that have the ability to continue to grow and divide in their nonspecialized state for long periods of time (e.g., months or years).
although the genes found within stem cells are the same, stem cells differentiate into unique cell types (e.g., muscle cells, nerve cells, etc.) due to
○ a. mutations in their genetic code.
○ b. different patterns in their gene expression.
○ c. meiotic division and fertilization.
○ d. random segregation and proliferation.

Explanation:

Gene expression refers to the process by which information from a gene is used in the synthesis of a functional gene product. Different cell types (like muscle and nerve cells) arise from stem cells because of differences in which genes are expressed (turned on) and which are silenced (turned off). Mutations (A) would change the genetic code itself, which is not the case here as the problem states the genes are the same. Meiotic division (C) is related to gamete formation in sexual reproduction and fertilization combines gametes, neither relevant to stem - cell differentiation. Random segregation (D) is more related to processes like chromosome separation in cell division (e.g., meiosis) and not the cause of stem - cell differentiation into specific cell types.

Answer:

B. different patterns in their gene expression.