Class 12 Biology - Genetics and Evolution

Activities

Activity 2.1: DNA Isolation from Plant Material

Aim/Objective: To isolate DNA from a given plant sample (like onion or banana).

Materials Required:

• Plant material (Onion, Banana, or Spinach)
• Detergent (liquid soap)
• Common salt
• Ice-cold ethanol or isopropanol
• Pestle and mortar
• Filter paper or fine cloth
• Beakers and glass rod

Procedure:

1. Crush the plant material thoroughly in a mortar with a little salt and water.
2. Add a few drops of liquid detergent to the paste and mix gently.
3. Filter the mixture into a beaker using a fine cloth or filter paper.
4. Carefully pour ice-cold ethanol along the side of the beaker.
5. Observe the interface between the ethanol and the filtrate.

Observation:

• Fine, white, thread-like fibers precipitate out into the ethanol layer. This is the isolated DNA.

Explanation:

• Crushing breaks the cell walls. Detergent dissolves the cell and nuclear membranes (which are made of lipids), releasing the DNA. Salt helps to neutralize the DNA's negative charge, allowing it to aggregate. DNA is insoluble in cold ethanol, so it precipitates as visible fibers.

Conclusion:

• DNA can be extracted from plant tissues using simple chemical and physical methods.

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Activity 2.2: Observing Mitosis in Onion Root Tips

Aim/Objective: To study the different stages of mitosis in plant cells.

Materials Required:

• Onion root tips
• Acetocarmine stain
• 1N HCl
• Microscope slides and cover slips
• Spirit lamp
• Microscope

Procedure:

1. Place a few onion root tips in 1N HCl for a few minutes to soften the tissues.
2. Transfer a root tip to a slide and add a drop of acetocarmine stain.
3. Warm the slide gently over a spirit lamp (do not boil).
4. Place a cover slip and squash the root tip by pressing firmly with the thumb or a pencil eraser.
5. Observe under the microscope.

Observation:

• Different stages of the cell cycle, such as Prophase, Metaphase, Anaphase, and Telophase, can be seen with distinct chromosome arrangements.

Explanation:

• Root tips are regions of active cell division (meristematic tissue). HCl breaks down the middle lamella, allowing the cells to be separated. Acetocarmine is a basic stain that binds specifically to the acidic DNA in chromosomes, making them visible under the microscope.

Conclusion:

• Mitosis is a continuous process of cell division that can be clearly visualized in rapidly growing plant tissues.