Answer:
The questions in this write up are three (3).
1. False
2. 24 DNA molecules
3. A check that chromosome replication has been successfully completed
Explanation:
QUESTION 1:
The cell cycle generally consists of two distinct phases viz: the Interphase and the Mitotic (M) phase. The Interphase is the phase where the cell undergoes rest and prepares for mitosis in the M phase. The Interphase comprises of the G1, S and G2 stages. As rightly said in the question, Mitosis, which is the division of the nuclear material, occurs in the M phase of the cell cycle but it occurs in a shorter time than the interphase.
The cell spends most of its time preparing for division in the Interphase i.e. enlarging, synthesing new DNA molecule etc.
QUESTION 2:
Each unreplicated chromosome contains one genetic material (DNA). The DNA content becomes doubled when the cell of an organism undergoes DNA replication in the S-phase of the cell cycle i.e. it becomes a replicated chromosome or sister chromatids.
According to the question, the animal species contains 6 pairs of chromosomes, meaning it will contain 12 unreplicated chromosomes with 12 DNA molecules prior to DNA replication. DNA replication has already occured in the G2 phase, hence, the cell will contain 12 sister chromatids will each chromatid containing 1 DNA molecule each. Therefore, 12 pair of sister chromatids or replicated chromosomes will contain 24 DNA molecules.
QUESTION 3:
During the cell cycle, certain internal control activities occur to ensure that each step of the cycle is going as planned. These mechanisms are called CHECKPOINTS. Each stage of the cell cycle is characterized by distinct checkpoints.
The checkpoints that occur after the G1 stage of interphase does not include checking the successful completion of DNA replication as placed in the question. DNA replication occurs in the S-phase of the cell cycle, which is the phase after G1, hence, at the G1 level, the cell is not expecting replication to have occured. The complete chromosome replication is checked at the G2 checkpoint.
