This happens when two chromosomes pair up and exchange segments of DNA. Why is crossing over an important part of meiosis?

Which mantle is under the crust the upper mantle or the lower mantle i think it's upper let me know if i'm right

1) what three conditions must be present for minerals to form through natural processes? 2) why are minerals considered inorganic substances? 3) how do oxides differ from other minerals that contain oxygen atoms? 4) how is a sulfide different from a sulfate? what makes native elements unique?

When a human or animal consumes food, the carbon in that food is most likely to be converted into which of the following elements? a. carbon remains carbon b. nitrogen c. oxygen d. hydrogen