Numerical Problems/ISC/Class 11
Created by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
Created by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
Numerical Problems - Cell Cycle and Cell Division
Question 1: A diploid cell has a DNA content of 4C and 20 chromosomes in the G2 phase. What would be the DNA content and chromosome number in the daughter cells after mitosis?
Solution: Mitosis is an equational division. The daughter cells will have the same chromosome number as the parent cell in G1. In G2, the cell has replicated its DNA, so it has 4C DNA and 2n chromosomes (where each chromosome has two chromatids). After mitosis, the daughter cells will be in G1 and will have a DNA content of 2C and a chromosome number of 2n = 20.
Question 2: If a human cell (2n=46) has a C-value of 3.2 pg, what is the DNA content (in pg) of a cell in Prophase I of meiosis?
Solution: The C-value represents the DNA content of a haploid nucleus (n). A diploid cell in G1 has a DNA content of 2C. Before meiosis I, the cell goes through S phase, where the DNA content doubles to 4C. Therefore, a cell in Prophase I of meiosis has a DNA content of 4C. 4C = 4 * 3.2 pg = 12.8 pg.
Question 3: A cell from an organism has 16 chromosomes and a DNA content of 20 pg in the G1 phase. What will be the number of chromosomes and DNA content in the G2 phase?
Solution: In the G1 phase, the cell has 2n chromosomes and 2C DNA content. So, 2n = 16 and 2C = 20 pg. In the S phase, the DNA replicates, so the DNA content doubles, but the chromosome number remains the same (each chromosome now has two chromatids). In the G2 phase, the number of chromosomes will still be 16, and the DNA content will be 4C = 2 * 20 pg = 40 pg.
A diploid somatic cell of an organism has 2n = 46 chromosomes and 2C amount of DNA in G1 phase. What will be the number of chromosomes and the amount of DNA in this cell after S phase and after Telophase of Mitosis?
Solution:
G1 Phase:
After S Phase (G2 Phase): DNA replication occurs, but the number of chromosomes (centromeres) remains the same. Each chromosome now consists of two sister chromatids.
After Telophase of Mitosis (in each daughter cell): The sister chromatids separate, and the cell divides, resulting in two identical diploid daughter cells.
Consider a diploid cell with 2n = 4 chromosomes and 2C amount of DNA in G1 phase. What will be the number of chromosomes and the amount of DNA in the cell at the end of Meiosis I and at the end of Meiosis II (in each daughter cell)?
Solution:
G1 Phase:
After S Phase (before Meiosis I): DNA replication occurs.
End of Meiosis I (in each daughter cell): Homologous chromosomes separate. The cell becomes haploid in terms of chromosome number, but each chromosome still has two chromatids.
End of Meiosis II (in each daughter cell): Sister chromatids separate. The cell remains haploid, and the DNA content is halved.
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