Final answer:
The Lyon hypothesis explains the random inactivation of one X chromosome in female mammalian embryos. X inactivation occurs early in development and is passed down to descendant cells, resulting in a consistent inactive X chromosome across all cells derived from the same progenitor cell. However, the hypothesis does not state that X inactivation is passed down during mitosis.
Step-by-step explanation:
The correct answer is B) X inactivation is passed down during mitosis.
The Lyon hypothesis, proposed by Mary Lyon, explains how one of the X chromosomes in a female mammalian embryo is randomly inactivated early in development. This inactivation occurs through a molecular process known as X inactivation. The inactivated X chromosome, also known as the Barr body, is then passed down to descendant cells, resulting in a consistent inactive X chromosome across all cells derived from the same progenitor cell.
However, the hypothesis does not state that X inactivation is passed down during mitosis. Mitosis is a process of cell division that produces identical daughter cells with the same genetic information. X inactivation occurs during early development, prior to mitosis, and the inactivated X chromosome is subsequently inherited by all descendant cells during subsequent divisions.