In the experiment, onion root tips are choosen to be observed under microscope. It is because the chromosomes are larger than most of the others plants. The root tips of onion are picked to observed as the root tips are the region where the cell division occurs mostly. The cells at the tips of the onion are actively dividing, therefore they are always in stages of mitosis. The tips on the slide are squashed with the aim to show a better and clearer observation of the chromosomes of individual cells. Adding Feulgen stain is to visualize the onion root tip cells.
Normally the chromosomes are not visible in nondiving cells because the DNA is still uncoiled. After adding Feulgen stain, supercoiling of the chromosomes into a highly compacted form happen. The supercoiled chromosomes are formed so that the chromosomes can be visualized under microscope. Be precautious when treating with Felgen stain because it is a type of DNA specific stains and carcinogens. Gloves should be wore. Based on the results, it shows that interphase is the most abundantly stage that is found in onion root-tip cells, and is followed by prophase.
The other phase: metaphase, anaphase and telophase only show lower amounts. The larger amount of interphase shows that the duration taken in interphase is longer than other phases. Interphase is a stage for the growth and also development of the cells. Majority of the cells are in interphase as replication of genetic material,DNA and organelles for production of new cells take a longer time. Prophase is the common phase after interphase. More times is needed for the process of condensing of sister chromatids into chromosomes. During prophase, mitotic spindles are developed from microtobules that produced by centrosomes too.
During this phase, the cell’s DNA replicates. G2 is a gap between the synthesis of DNA and beginning of mitosis. It is a period of rapid cell growth and synthesis of protein. During prophase, the chromatins super coiled and become thicker and shorter. Thickening continues till they condense into chromosomes. Each chromosomes has been duplicated, consists of two sister chromatids. Soon, the spindle which is made up of microtubules start forming. The disintegration of nuclear envelope and nucleoli occur. At metaphase, the chromosomes have moved to the center of the nucleur.
The chromosomes have aligned at the metaphase plate and the centromeres of each sister chromatids, chromosomes have attached to the spindle. The nuclear membrane disintegrates totally at the same time. The centromeres are divided during anaphase. Sister chromatids are seperated and pulled to the corresponding poles by the spindle fibres. While the telophase is the last stage of mitosis division. A new nuclear envelope is formed around each group of chromosomes. The chromosomes uncoil. The nucleoli and nuclear envelope are formed and reappearred again. The cytoplasm is divided equally and two daughter cells are produced.