Q.65 A cell in G1 of Interphase has 12 chromosomes. In Anaphase–I of meiosis, the number of
DNA molecules per cell will be__________

A cell in G1 interphase with 12 chromosomes (diploid, 2n=12) undergoes DNA replication in S phase, doubling the DNA content before meiosis begins. By Anaphase I of meiosis, homologous chromosomes separate to opposite poles, but each chromosome still consists of two sister chromatids (one DNA molecule each), resulting in 24 DNA molecules per cell.​

Step-by-Step Progression

DNA replication occurs once during interphase S phase, converting each of the 12 chromosomes (one chromatid each) into 12 chromosomes with two sister chromatids, yielding 24 DNA molecules.​

Homologous pairing and crossing over happen in Prophase I and alignment in Metaphase I, maintaining 12 chromosomes (24 DNA molecules).​

In Anaphase I, homologues separate (6 chromosomes, each with 2 chromatids, to each pole), but the single cell contains all 24 DNA molecules until telophase/cytokinesis.​

In a G1 interphase cell with 12 chromosomes entering meiosis, understanding the number of DNA molecules in Anaphase I of meiosis is crucial for CSIR NET life sciences aspirants tackling cell cycle and meiosis questions. This query tests knowledge of DNA replication timing and chromatid separation mechanics.​​

Meiosis Basics and DNA Replication

Meiosis reduces chromosome number for gamete formation, starting after interphase. In G1, the cell has 12 chromosomes (24 chromatids post-S phase replication, as each chromatid holds one DNA molecule). S phase doubles DNA without changing chromosome count, setting 24 DNA molecules through Meiosis I.​

Stages Leading to Anaphase I

• Prophase I: Homologous chromosomes (12 total) pair as tetrads; 24 DNA molecules persist with crossing over.​

• Metaphase I: Tetrads align at equator; still 12 chromosomes, 24 DNA molecules.​
  No DNA replication occurs between Meiosis I and II.​

Anaphase I Details

Homologous chromosomes separate to poles (no sister chromatid split yet), but the undivided cell retains all 24 DNA molecules (12 chromosomes × 2 chromatids each). Post-cytokinesis, each daughter gets 12 DNA molecules.​

Common Exam Confusions

Students often mistake Anaphase I for chromatid separation (that’s Anaphase II) or forget replication yields 24 molecules total. For mitosis prophase, it matches (12 chromosomes, 24 DNA); Anaphase II post-split would differ.​​

This aligns with CSIR NET patterns on chromosome/DNA counting in cell division.​