Why were plasmids injected into silkworm eggs rather than directly into the silkworms themselves?

• A. If injected into eggs, the gene gets into all / most of cells of silkworm
• B. It is easier to inject into eggs
• C. It prevents the gene from integrating
• D. It glows without plasmid

Answer: (A)

The key idea is germline, whole-body transformation. Injecting the plasmid into the silkworm egg (the one-cell zygote stage) lets the foreign DNA be present as the organism develops, so it can be propagated into most or all cells, including the germline. That broad distribution means the trait appears throughout the body and can be inherited by offspring. If the DNA were injected into an already developed silkworm, only a subset of cells that happen to take up the DNA would carry the gene, leading to a mosaic organism with limited, non-heritable expression. The other choices don’t capture why early-stage injection is used: ease of injection isn’t the primary goal, preventing integration isn’t desirable for a stable trait, and glowing without the plasmid isn’t relevant to why eggs are used.