Magnetic 3D-Printed Chromosome Models - Mitosis and Meiosis

Introduction

These are models of chromosomes, centromeres and spindle fibres that I made in order to help me better understand mitosis and meiosis, especially chromosomal crossover.

I wanted the model to have these properties:

1. The centromeres of sister chromatids should be magnetic so that they should be able to stick together in metaphase but also be pulled apart to demonstrate anaphase.
2. The centromeres should have a hole so that a hook, representing the spindle fibres/microtubules, can slip into the hole and can be used to pull apart the sister chromatids during anaphase.
3. The chromosomes should have chiasma which may be swapped between homologous chromosomes to show chromosomal crossover.

Detailed instructions and assembly video on Instructables: Instructables project

Onshape documents of the models: Onshape centromere model, Onshape chiasma model

Supplies

You will need:

1. A 3D printer - I used an Ender 3 S1, which is a FDM printer, but you can use a resin printer.
2. A filament spool or resin for the 3D printer. I used PLA, but any rigid filament or resin should work
3. Circular magnets - 1.5mm thick with a 5.9mm diameter. (The magnets should be axially magnetized, which means that the opposite faces have opposite poles. )
4. Wire pipe cleaners / chenille stems, those used for arts and crafts, of different colors.
5. A hot glue gun.
6. Large popsicle sticks.

Print settings

Slice and print the attatched STLs. I used Cura 5.4.0. Use these settings:

1. Layer height: 0.28 mm
2. Walls: 2 walls
3. Infill: 10%, Lightning or Cubic

No support or build plate adhesion is needed, if printed in the orientation shown.

Print 2 centromeres and 2 chiasmas per "set" (a pair of sister chromatids).

Assembly

Step 1: Glue the Magnets to the Plastic Pieces

1. Attach the magnets to the plastic pieces with hot glue. Ensure the magnet poles are facing the correct direction, as shown in the images.
2. Glue one magnet with the north pole facing outwards and one magnet with the south pole facing outwards in each centromere piece.
3. Glue one magnet with the north pole facing outwards and one magnet with the south pole facing outwards per pair of chiasma.

Step 2: Thread Pipe Cleaners Through the Plastic Pieces

1. Take 2 centromere pieces, 2 chiasma pieces, and 2 whole pipe cleaners.
2. Cut the two whole pipe cleaners into 3 half-pieces and 2 quarter-pieces.
3. Thread two of the half-pieces into the holes of one centromere piece. Thread the last half-piece and one quarter-piece into the holes of the other centromere piece.
4. Then thread the ends of both quarter pieces through one chiasma each.

If you are making more than one "set", ensure that the magnet polarity of both pairs of chiasma are facing the same way - refer to the images. Visit my Instructables page for the assembly video.

Step 3: Make the Spindle Fibres and Centrosomes

1. Cut a large popsicle stick into parts 4 cm long.
2. Drill two holes at the ends of each part.
3. Thread and tie a pipe cleaner through each of the two holes and bend the ends into hooks.

Step 4: Conclusion

Have fun with your new chromosome models! Go out and share them with your fellow teachers, students and friends.