What is the order of the cellular levels from smallest to largest

What would be the result if crossing over did not happen during meiosis in humans? a. there would be less genetic variation in humans. b. parents would be more likely to look like their children. c. the human population could not reproduce. d. children would have more chromosomes.

Acquired mutations can result from radiation pollution toxins inheritence select all that apply

Several billion years ago which gas was the least prevailant in the atmosphere