2
Question
You have studied mitosis in onion root tip cells. It has 16 chromosomes in each cell. Can you tell:
(i) How many chromosomes will the cell have at the G1 phase, after S phase, and after M phase?
(ii) Also, what will be the DNA content of the cells at G1, after S and at G2, if the content after M phase is 2C?
(i) How many chromosomes will the cell have at the G1 phase, after S phase, and after M phase?
(ii) Also, what will be the DNA content of the cells at G1, after S and at G2, if the content after M phase is 2C?
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Solution
Step 1: G1 phase.
In the G1 phase, the cell is metabolically active.
Number of chromosomes per cell given =16
Number of the chromosome per cell at G1 phase =16.
Step 2: S phase.
S phase is also known as the synthesis phase. It is marked by DNA
replication. During this time, the amount of DNA per cell doubles without
any increase in the chromosome number.
Number of the chromosome per cell after S phase =16.
Step 3: M phase.
M phase represents the phase in which the actual cell division occurs. During mitosis, the chromosomes containing two chromatids each with one DNA molecule splits into two separate chromatids, and each chromatid behaves as a future daughter chromosome. At the end of the M phase, both daughter cells formed contain an equal number of chromosomes as was present in the parent cell.
The number of chromosomes per cell at the beginning of the M phase =16
The number of chromosomes after the M phase (here, mitosis) per daughter cell =16.
Final answer:
Onion is diploid with 16 chromosomes. During the cell cycle, the number of chromosomes at G1 and after S are 16 each. Also, after the M phase (after mitotic cell division), the number of chromosomes in each daughter cell is 16.
Step 1: G1 phase.
This phase is also known as pre-DNA synthesis phase. In this phase, the cell prepares itself for DNA replication by forming proteins involved in the replication machinery.
Considering the DNA content present in a diploid onion cell to be 2C, the DNA content per cell at G1 phase is 2C.
Step 2: S phase.
In this phase, the amount of DNA per cell doubles. Considering the initial amount of DNA to be 2C per cell, it increases to 4C after DNA replication
Step 3: G2 phase.
Synthesis of proteins occurs in the G2 phase to make the cell ready for M phase. Hence, the amount of DNA per cell at G2 phase is 4C.
Final answer:
The amount of DNA per cell at G1 phase, after S phase and at G2 phase is 2C,4C and 4C respectively
In the G1 phase, the cell is metabolically active.
Number of chromosomes per cell given =16
Number of the chromosome per cell at G1 phase =16.
Step 2: S phase.
S phase is also known as the synthesis phase. It is marked by DNA
replication. During this time, the amount of DNA per cell doubles without
any increase in the chromosome number.
Number of the chromosome per cell after S phase =16.
Step 3: M phase.
M phase represents the phase in which the actual cell division occurs. During mitosis, the chromosomes containing two chromatids each with one DNA molecule splits into two separate chromatids, and each chromatid behaves as a future daughter chromosome. At the end of the M phase, both daughter cells formed contain an equal number of chromosomes as was present in the parent cell.
The number of chromosomes per cell at the beginning of the M phase =16
The number of chromosomes after the M phase (here, mitosis) per daughter cell =16.
Final answer:
Onion is diploid with 16 chromosomes. During the cell cycle, the number of chromosomes at G1 and after S are 16 each. Also, after the M phase (after mitotic cell division), the number of chromosomes in each daughter cell is 16.
Step 1: G1 phase.
This phase is also known as pre-DNA synthesis phase. In this phase, the cell prepares itself for DNA replication by forming proteins involved in the replication machinery.
Considering the DNA content present in a diploid onion cell to be 2C, the DNA content per cell at G1 phase is 2C.
Step 2: S phase.
In this phase, the amount of DNA per cell doubles. Considering the initial amount of DNA to be 2C per cell, it increases to 4C after DNA replication
Step 3: G2 phase.
Synthesis of proteins occurs in the G2 phase to make the cell ready for M phase. Hence, the amount of DNA per cell at G2 phase is 4C.
Final answer:
The amount of DNA per cell at G1 phase, after S phase and at G2 phase is 2C,4C and 4C respectively
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