Question

Which statement is correct?
All cells have the same genes, and all of a cell's genes are active at the same time.
All cells have the same genes, but different genes are active in different cells.
As cells and tissues differentiate, they lose the genes they do not need.
Eyes look different than a liver because the cells that make up these organs have different genes.

Answer 1

"All cells have the same genes, but different genes are active in different cells." is correct.

Brief explanation:
- In a multicellular organism, almost every cell contains the same DNA (same set of genes). Different cell types arise because different subsets of those genes are turned on or off (gene expression), controlled by regulatory and epigenetic mechanisms.
- Why the others are wrong:
- Not all genes are active at the same time—cells only express the genes they need.
- Differentiating cells generally do not lose genes; they silence genes they don't need rather than deleting them (exceptions exist, e.g., enucleated red blood cells, immune-cell DNA rearrangements).
- Eyes and liver look different not because their cells have different genes, but because their cells express different programs of the same genome.