Aiko looks at a cell in the root tip of an onion…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Aiko looks at a cell in the root tip of an onion. It has chromosomes and C of DNA in G1 phase. It goes through S phase and G2 phase.
- How many chromatids does the cell have at the end of G2?
- What is the DNA content at the end of G2, in units of C?
- The cell divides by mitosis. How many chromosomes does each daughter cell have?
- What is the DNA content of each daughter cell, in units of C?
Need a reminder? The key ideaShow
A human cell in culture takes about 24 hours to go round the cycle: G1 about 11 h, S about 8 h, G2 about 4 h and M about 1 h. Interphase is G1, S and G2. S phase raises the DNA from 2C to 4C and gives every chromosome a second chromatid. The number of chromosomes stays 2n.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. , DNA C in G1.
Plan. Follow the chromosomes and the DNA from G1 to the daughter cells.
Step 1. Chromatids. There are chromosomes, and each has two chromatids after S phase. chromatids.
Step 2. DNA in G2. S phase doubles the DNA. C.
Step 3. Daughter cells. Mitosis is equational. Each daughter cell has chromosomes.
Step 4. DNA of a daughter cell. The C is shared equally. Each daughter cell has C.
Answer: chromatids; C; chromosomes; C.
Check. The two daughter cells together hold C, the same as the parent in G2.
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