Meiosis Prophase I: After each chromosome has replicated during interphase, each pair of homologous chromosomes pairs up during Prophase I to form synaptonemal complexes where crossing over can occur. In the diagram below, the "mother cell" that is just entering meiosis is heterozygous at two gene loci (genotype: A/a;B/b).

Select from the four chromosomes shown at left two copies of chromosomes and drag each these copies to the appropriate positions (P1 or P2) next to appropriate homologous chromosome. If you choose correctly (there is only one correct choice for P1 and one for P2), a congratulatory message will appear, and the yellow box will become green. If you choose incorrectly, you will be asked to try to make another choice. You may restart at any time by reloading the webpage.

Please try to explain why only some arrangements of chromosomes are possible.