Cell Cycle and Cell Division

Biology · Class 11

Simulation · Biology · Class 11

Count the chromosomes and the DNA

"Count the chromosomes and the DNA" is a free, interactive Class 11 Biology simulation for NEET, built on the lesson "Meiosis II" in Cell Cycle and Cell Division. This cell has 2n = 4: a long and a short pair, blue from one parent and amber from the other. Slide through the stages and watch the four counts. Count a chromosome by its centromere (the black dot). S phase doubles C, never n. Mitosis splits chromatids once, so 2n stays 2n. Meiosis I separates homologues (2n to n) and meiosis II separates chromatids (2C to C), with no copying in between.

From the lesson Meiosis II in Cell Cycle and Cell Division. Change the values and watch what happens.

Count the chromosomes and the DNABiology · Class 11

The idea behind it

NCERT §10.4.2

  • Meiosis II begins straight after cytokinesis, generally while the chromosomes are still not fully stretched out. Unlike meiosis I, it resembles an ordinary mitosis.
  • Prophase II: the chromosomes become compact again, and the nuclear membrane has disappeared by the end of this stage.
  • Metaphase II: the chromosomes line up at the equator, and microtubules from opposite poles attach to the kinetochores of the sister chromatids.
  • Anaphase II: the centromere of each chromosome, which had been holding the sister chromatids together, splits simultaneously in all chromosomes, and the chromatids move to opposite poles as the microtubules attached to the kinetochores shorten.
  • Telophase II: the two groups of chromosomes are enclosed by nuclear envelopes again, and cytokinesis follows, giving a tetrad of cells, four haploid daughter cells.
  • Counting through it: a 2n cell with 4C DNA gives two cells of n chromosomes (2C each, chromatids still paired) after meiosis I, and four cells of n chromosomes (C each) after meiosis II.

Questions

2 answers

What does the "Count the chromosomes and the DNA" simulation show?
This cell has 2n = 4: a long and a short pair, blue from one parent and amber from the other. Slide through the stages and watch the four counts. Count a chromosome by its centromere (the black dot).
Is this simulation free?
Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Meiosis II" in Cell Cycle and Cell Division (Class 11 Biology).

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