Onion Root Tip Mitosis Virtual Lab

Theoretical Background

• The genetic information of plants, animals and other eukaryotic organisms resides in several (or many) individual DNA molecules, or chromosomes. For example, each human cell possesses 46 chromosomes, while each cell of an onion possesses 8 chromosomes. 
• All cells must replicate their DNA when dividing. During DNA replication, the two strands of the DNA double helix separate, and for each original strand a new complementary strand is produced, yielding two identical DNA molecules. DNA replication yields an identical pair of DNA molecules (called sister chromatids) attached at a region called the centromere.
• DNA replication in eukaryotes is followed by the process called mitosis which assures that each daughter cell receives one copy of each of the replicated chromosomes. 
• During the process of mitosis, the chromosomes pass through several stages known as prophase, metaphase, anaphase and telophase. The actual division of the cytoplasm is called cytokinesis and occurs during telophase.
• During each of the preceding stages, particular events occur that contribute to the orderly distribution of the replicated chromosomes prior to cytokinesis. 

The stages of mitosis can be broadly categorised into two parts: 

1. Karyokinesis (division of nucleus) 
2. Followed by cytokinesis (division of cytoplasm, and ultimately of the cell).

Those cells, which are not in the phases of cell division are considered to be in interphase. You may observe that most of the cells in a microscope field are in interphase.

Principle Of Work

• In the online onion root tip mitosis lab, students will observe the stages of mitosis by preparing a stained slide of onion root tip cells, which contain actively dividing cells ideal for study. 
• First, a small section of the root tip is cut and placed in a staining solution, which highlights the chromosomes for easier viewing.
• After heating gently to enhance staining, the root tip is squashed under a cover slip to spread the cells thinly. Under a microscope, students will then identify and observe the different stages of mitosis—prophase, metaphase, anaphase, and telophase—and note characteristic changes in chromosome alignment and separation. 
• This hands-on process, supported by mitosis simulations, provides insight into cell division and the distinct phases of mitosis.