The Following Question Refers to the Essential Steps in Meiosis

The following question refers to the essential steps in meiosis described below.
1. Formation of four new nuclei, each with half the chromosomes present in the parental nucleus
2. Alignment of tetrads at the metaphase plate
3. Separation of sister chromatids
4. Separation of the homologs; no uncoupling of the centromere
5. Synapsis; chromosomes moving to the middle of the cell in pairs
-Which of the following best describes the frequency of crossing over in mammals?

A) ~50 per chromosome pair
B) ~2 per meiotic cell
C) at least 1-2 per chromosome pair
D) ~1 per pair of sister chromatids
E) a very rare event among hundreds of cells