Q.30 The difference between mitosis and meiosis I is
(A) Sister chromatids separate in mitosis, whereas homologous chromosomes separate in meiosis I
(B) The nuclear membrane is absent during mitotic metaphase, but not in meiotic metaphase
(C) The DNA is double helical in meiosis I but not in mitosis
(D) Unlike in mitotic metaphase, chromosomes do not align at the equatorial plate in meiosis I
(A) Sister chromatids separate in mitosis, whereas homologous chromosomes separate in meiosis I
Correct Answer
Option (A) correctly identifies the key difference. In mitosis, sister chromatids separate during anaphase, producing identical diploid daughter cells. In meiosis I, homologous chromosomes separate during anaphase I, reducing the chromosome number to haploid while keeping sister chromatids together.
Option Analysis
(A) Correct
Sister chromatids separate in mitosis at anaphase, pulled to opposite poles by spindle fibers. Homologous chromosomes separate in meiosis I anaphase I, held by chiasmata until then, ensuring genetic diversity and ploidy reduction.
(B) Incorrect
Nuclear membrane breaks down before metaphase in both mitosis and meiosis I, absent during metaphase stages. Spindle assembly requires this breakdown in both processes.
(C) Incorrect
DNA maintains its double helical structure in both mitosis and meiosis I. No change in DNA topology occurs specific to either process.
(D) Incorrect
Chromosomes align at the equatorial plate (metaphase plate) in metaphase of both mitosis and meiosis I. Homologous pairs (bivalents) align in meiosis I, similar to individual chromosomes in mitosis.
The primary difference between mitosis and meiosis I lies in chromosome separation: sister chromatids separate in mitosis, while homologous chromosomes separate in meiosis I. This distinction is crucial for CSIR NET Life Sciences aspirants preparing for cell division questions.
Mitosis Overview
Mitosis produces two identical diploid cells for growth and repair. During anaphase, spindle fibers pull sister chromatids apart to opposite poles.
Meiosis I Overview
Meiosis I, the reduction division, halves chromosome number. Homologous chromosomes pair in prophase I, align as bivalents in metaphase I, and separate in anaphase I.
Key Comparison Table
| Feature | Mitosis | Meiosis I |
|---|---|---|
| Separating Units | Sister chromatids | Homologous chromosomes |
| Daughter Cells | 2 diploid | 2 haploid |
| Alignment in Metaphase | Individual chromosomes | Bivalents at equatorial plate |
| Nuclear Membrane | Absent in metaphase | Absent in metaphase I |
Exam Relevance
For CSIR NET, recognize that options testing nuclear membrane, DNA helix, or equatorial alignment are distractors. Focus on anaphase events for accurate differentiation.
