Inheritance – Mitotic Squash of Garlic Root Tip
Mitosis is the process of cell division; it is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets in two nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly equal shares of these cellular components. Mitosis and cytokinesis together define the mitotic phase of the cell cycle—the division of the mother cell into two daughter cells, genetically identical to each other and to their parent cell. The process of mitosis is complex and highly regulated. The sequence of events is divided into phases, corresponding to the completion of one set of activities and the start of the next. These stages are interphase, prophase, metaphase, anaphase and telophase. During mitosis the pairs of chromosomes condense and attach to fibers that pull the sister chromatids to opposite sides of the cell. The cell then divides in cytokinesis, to produce two identical daughter cells. In plants, growth is greatest at the shoot and root tips. Here mitosis occurs in particular areas called the meristems (a meristem is a tissue in all plants that consists of meristematic cells. These are cells that have not yet a special function. They are found in zones of the plant where growth can take place).
The cell is engaged in metabolic activity and performing it’s preparation for mitosis. DNA has replicated, but has not formed the condensed structure of chromosome. They remain as loosely coiled chromatin. The nuclear membrane is still intact to protect the DNA molecules from undergoing mutation. During interphase DNA in the nucleus doubles and new organelles, such as mitchondria, are made.
The chromosomes become visible as long thin threads, they start to coil up and become thicker and shorter and a spindle forms independently. Towards the end of prophase each chromosome consists of two chromatids held together by a centromere. The nucleolus then disappears and the nuclear envelope breaks down. Plants, Animals: Chromosomes condense.
Animals: mitotic spindle forms between centrosomes on one side of the nucleus.
Plants: cortical microtubules grow together to form the spindle around the nuclear envelope.
Microtubules assemble forming a spindle. The chromosomes move towards the equator of the spindle. They then attach themselves to a spindle fibre by means of a centromere.
Plants, Animals: Chromosomes align at spindle equator.
Centromeres divide and the kinetochore component of the centromere pulls the chromatids along the microtubule towards the poles. This movement results from the contraction of the spindle fibres, as they shorten they pull the chromatids apart.
Plants, Animals: Chromosomes move towards cell poles.
Chromatids have now reached the poles and are now distinct chromosomes. The nuclear envelope reforms around each group of chromosomes and the nucleolus reappears. The chromosomes uncoil and the spindle dissolves. The cytosplasm then divides by cytokinesis, which will produce two genetically identical daughter cells. Plants, Animals: Nuclear envelopes reform and chromosomes begin to decondense, spindle breaks down. Phragmoplast forms in center of cell, where new cell wall will be formed. Animals: Contractile ring forms approximately midway between the two nuclei in the dividing cell.
Firstly, vesicles that contain carbohydrates (such as hemicelluloses and pectins,) produced by the Golgi body collect on the equator. They fuse together to form a cell plate. The cell plate eventually stretches across the cell forming the middle lamella. Cellulose builds up on either side of the middle lamella to form the walls of two new cells. These cells are...