Select the correct option:Centrioles undergo duplication during _______(i) of ________(ii), and begin to move towards opposite poles of the cell during ________(iii) stage of _________(iv).
In animal cells, during the S phase of interphase, DNA replication begins in the nucleus and the centriole duplicates in the cytoplasm. These duplicated centrioles move towards opposite poles of the cell in prophase of mitosis.
______ is the best stage to count the number and study the morphology of chromosomes.
Metaphase is the best phase to count total number of chromosomes in any species and detailed study of morphology of chromosome. Idiogram (arrangement of chromosomes in a series of decreasing length) can be drawn in the stage.
At which stage of mitosis, the two daughter chromatids separate from each other, migrate towards the opposite poles and are now referred to as chromosomes of the future daughter nuclei?
In anaphase, the centromeres of chromosomes start to divide into two, forming daughter chromosomes with centromere in each. Daughter chromosomes are repulsive, so they migrate towards opposite poles. Spindle fibres attached to the centromeres shorten and pull the chromosomes to the poles.
During anaphasic movements of chromosomes, ______ of each chromosome is/are towards the pole and _____ of the chromosome trail(s) behind.
In anaphasic movement of chromosomes, the centromeres lead the path while the arms trail behind. As a result the anaphasic chromosomes appear V., L, J- and I-shaped. The shapes are formed respectively in metacentric, submetacentric, acrocentric and telocentric chromosomes.
Which of the following statements is not correct regarding colchicine?
Colchicine is an alkaloid widely used in plant breeding for doubling the chromosome number. The alkaloid does not allow the formation of spindle because it prevetns assembly of microtubules. It is, therefore, called 'mitotic poison'. Colchicine holds holds the cells in metaphase. Colchicine does not inhibit chromosome replication.
What is true about telophase stage of mitosis?
During telophase, the individual chromosomes are no longer seen and chromatin material tends to collect in a mass at the two poles. Chromosomes cluster at opposite spindle poles and their identity is lost as discrete elements. Nuclear envelope assembles around the chromosome clusters. Nucleolus, Golgi complex and ER reform.
Spindle usually persists in the form of ______ during _____ method of cytokinesis.
In higher plants cytokinesis is takes place by cell plate method. In this method small vesicles of Golgi complex are assembled at the equator. Here spindle persists for some time called phragmoplast. All vesicles fuse to form two sheets which enclose a matrix or film. This film becomes solidified to form cell plate or middle lamella. It grows centrifugally and finally comes in contact with lateral walls of parent cell. Now phragmoplast disappear. Cellulose, hemicellulose and pecting are deposited on either side of cells plate. It forms primary cell wall.
The best material for studying mitosis in the laboratory is
The sites of mitotic cell division in a plant are meristematic regions. Mitosis can be easily studied in smears of root and stem tips. Which contain rapidly dividing apical meristems.
Mitotic spindle is mainly composed of _________ protein.
Spindle fibres are structures formed from mictrobubules in the cytoplasm during cell division. Microtubules are made up of tubulin protein. Spindle fiberes move chromatids or chromosomes diametrically apart and gather them in two d=clusters at opposite ends (poles) of the cell.
Microtubules are absent in
Microtubule is a microscopic tubular structure, with an external diameter of 24 nm and of variable length, found in a wide range of eukaryotic cells. Microtubules are composed of numerous subunits of the globular protein tubulin and occur singly or in pairs, triplets, or bundles. Microtubules help cells to maintain their shape. They also occur in cilia and eukaryotic flagella and the centrioles and form the spindle during nuclear division. A further role is in the intracellular transport of materials and movement of organelles.
During cell division, the spindle fibres get attached to condensing chromosome at a highly differentiated region. This region is called as
The key feature of metaphase is the attachment of spindle fibers to kinetochores of chromosomes. Kinetochores are disc-shaped structure at the surface of the centromeres. These structures serve as the site of attachment of spindle fibres to the chromosomes that are moved toward poles.
If the tissue has at a given time 1024 cells, how many cycles of mitosis had the original parental single-cell undergone?
Each cycle produces 2 daughter cells. It is calculated by the formula (2number of cycles= number of daughter cells). Ten cycles are required to produce 1024 cells as follows:
210 = 1024.
Which phase of mitosis is essentially the reverse of prophase in terms of nuclear changes?
During telophase of mitosis viscosity of cytoplasm decreases. A new nuclear membrane is formed (either from older nuclear envelope or ER) around each set of chromosomes. Chromosomes overlap farming chromatin. The nucleolar organiser region of satellite chromosomes produce nucleolus for each daughter nucleus. Nucleoplasm surrounds in the area of chromatin. The gel state of spindle is converted into sol state and disappears. In this way two daughter nuclei are formed at the poles of spindle. Hence this phase is just reverse of prophase.
The given graph shows the change in DNA content during various phases (A to D) in a typical mitotic cell cycle. Identify the phases and select the correct option.
During G1 phase, DNA content is 2C.S phase is marked by replication of DNA and the amount of DNA per cell is doubled. During G2 phase, synthesis of RNA and proteins takes place. During mitosis, DNA content gets equally distributed among two daughter cells.
A cell's division time is 1 minute. In 20 minutes, a culture tube (culture medium) is 1/8th filled with cells. When the tube will be fully filled?
In 20 mins. Culture tube 1/8th filled with cells. Each cell divides every minute producing two daughter cells.
Hence, 21 min = 1/8 × 2 = 1/4
In 22 min 1/4 × 2 = 1/2
In 23 min 1/2 × 2 = 1
That means, in 23 minutes the culture tube will be completely filled.
In above sequence of figures showing different stages of cell division, the missing stage (ii) is
Figure (i) shows metaphase II and figure (iii) shows telophase II, Hence, the missing figure is that of anphase II.
The separation of two chromatids of each chromosome at early anaphase is initiated by
Kinetochore is a plate-like structure by which microtubules of the spindle attach to the centromere of a chromosome during nuclear division. The centromere of each chromosome divides into two, so that each chormatied comes to have its own centromere. The two chromatids now start repelling each otherand separate completely to become daughter chromosmes. the daughter or new chromosmes. The daughter or new chromosomes move towards the poles of spindle along the path of their chromosome fibres.
Cell would normally proceed to mitosis without interruption
The availability of mitogen and energy rich compounds decide wheter G1 phase will be arrested (G0 phase) or undergo S-phase. This point is called check point or G1 cyclin or G1 point. Once the check point of G1-phase is crossed and cell has entered S-phase, cell cycle will go on further division till completion.
Amitosis usually occurs in
Amitosis is a method of direct cell division in which the nucleus divides into two daughter nuclei without showing differentiation of chromosomes and development of spindle. It is commonly seen in prokaryotes.
The role of mitosis is not merely to divide a cell into two daughter cells but to ensure genetic continuity from one cell generation to another cell generation. The mechanism ensuring genetic continuity is
All the daughter cells of multicellular organism have the same number and type of chromosomes as parent cells due to equitable distribution of all chromosomes in mitosis. This helps in ensuring genetic continuity.