Monozygotic twins arise from a single embryo whose cells divide into two groups within about how many days of zygote formation?

1. Monozygotic twins come from one embryo. 2. Its cells split into two groups during early development, within 8 days of zygote formation. 3. Each group develops as a separate embryo, giving identical twins of the same gender. 4. A split after 8 days risks conjoined twins, and 28 days, 90 days and 9 months are unrelated spans, so those are ruled out. _Source: Balbharati (Maharashtra Board) Class 10 Science & Technology Part 2, Ch 3 "Life Processes in Living Organisms Part 2", p.42_