Question

For this question, you will create a drawing that you should upload as an image. (1 bonus point will be awarded for neat and clear images that do not show more than the requested information.)

Imagine a haploid eukaryotic cell with a genome consisting of two unique chromosomes. The cell enters the cell cycle and divides by mitosis. Its daughters also enter the cell cycle and divide by mitosis to create granddaughter cells.

1) Draw the original cell in the G1 phase of the cell cycle as a circle with the chromosomes represented as double-stranded DNA molecules.

2) Below the first cell, draw all the daughter cells in G2 phase of their cell cycle using the same representation.  

3) Below the daughter cells, draw all the granddaughter cells in G1 phase of their cell cycle.

4) Write the combined total number of chromatids that will be present in both daughters when they are at the beginning of M phase next to your picture of the daughter cells.

5) Could one or more of the granddaughter cells contain an entire DNA strand that was present in the G1 phase of the cell that you drew for (1)? (Not a copy of the strand, but the actual molecule.) Write your one-word answer next to the granddaughter cells.

6) Highlight or label your diagram to justify your answer to (5).

Answer 1

Remember that the genome is not replicated in G1 stage but it actually IS in G2, so the original cell and the granddaughters will appear with a single copy, but the daughter cells will appear with 2 sister chromatides:

5.- No, because DNA replication is semiconservative, each single strand from the beggining segregated into different daughter cells, and again segregation occurred when daughter cells divided.

6.- We are going to color the DNA molecules, the original ones are going to be red, the ones produced for the first mitotic event will be blue, and the ones produced by the second mitotic event will be magenta:

As you can see, there is no possibility for any grandaughter cell to have 2 red single strands in any double stranded chromosome