Mitosis Prophase I: Imagine a heterozygous cell (genotype A/a) just beginning the process of mitosis. For simplicity, we will only look at a single pair of homologous chromosomes. During interphase, each chromosome has been replicated, and the picture below shows the two sister chromatids joined together at the centromere.

Start by dragging one of the allele markers to one of the positions (P1 to P4) on any of the chromosomes. When you drop the label and click, you should see the box underneath the marker turn green. Next think about which of the other chromosomes can have either the recessive allele (a) or the dominant one (A). If you try dropping an allele marker onto a spot where it is possible, the box underneath will turn green. If not, the box will stay yellow and you will be given another chance to place the allele marker onto another position. You may restart at any time by reloading the webpage.

Please try to explain why only some arrangements of chromosomes are possible due to the replication of chromosomes during interphase. Compare what happens during prophase of meiosis, when homologous chromosomes pair and crossing over can happen during formation of synaptonemal complexes.