Cell division is an essential process in all eukaryotic organisms. It allows body cells to multiply in number and generate gametes for reproduction. Students can observe onion root tip cells during mitosis to gain insight into this biological process. Onions make an ideal topic as their active-dividing cells make this experiment all the easier, plus dyes may enhance contrast for better viewing of chromosomes and their positions on cell nuclei.
Begin the experiment by gathering onion roots from an actual living plant, cutting off one root tip, and floating it in a solution of aceto orcein stain – an opaque dark colorant which stain chromatin during different phases of mitosis and visible under microscope. Aceto orcein works by binding to histone proteins within chromatin; visible to naked eyes but identifiable under microscope as multiple levels of coiled structures that look like chromosomes.
Interphase cells do not exhibit visible chromosomes as their DNA exists in long threads that resemble strings, making interphase chromosomes indiscernible under a microscope. When entering mitosis, however, their chromosomes become visible due to condensing into distinct coiled structures which become visible near the center of each cell. At this time, DNA present in their nucleus divides into two equal portions known as sister chromatids which then move towards opposite poles where they will finally disassemble to become daughter cells.
Each daughter cell inherits an equal number of chromosomes from its mother cell during karyokinesis and cytokinesis; once completed, daughter cells can begin growing on their own to complete cell division.
Onions have long been used as a model for studying chemical and radiation-induced chromosomal aberrations (CAs), an indicator that genetic material has been damaged. Common onion (Allium cepa) root tip cells are the preferred choice due to their small size, low spontaneous aberration frequency and stable number of chromosomes.
While some might view it as unnecessary, many others see value in using their expertise to bring value-add services directly into their own communities. To determine whether commercially available cigarettes retained cigarette smoke components responsible for mitotic abnormalities in onion (Allium cepa) root-tip cells, a water-soluble extract of tobacco smoke condensate (TSC) was prepared and evaluated on their cytology. Results revealed that TSC from both types of cigarettes tested did not contain any compounds responsible for mitotic irregularities in onion cells, even at higher concentrations. This finding suggests that filters used in cigarette production fail to adequately protect onion root-tip cells from exposure to genotoxic agents, and may serve as useful markers of industrial effluents before being released into the environment.