Which two substances bind using a lock-and-key mechanism?

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.

Explain how paleontologists use trilobite fossils as index fossils for various geologic time periods.

Compare the shapes of the bones of the human skull with the shapes of the bones of the human leg. how do the shapes differ? why are the shapes important?