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Select the correct option with respect to mitosis.
In metaphase of mitosis, spindle fibres attach to kinetochore of chromosomes. Chromosomes are moved to spindle equator and get alligned along metaphasic plate through spindle fibres to both pole.
Astral rays arise from
(a) Astral rays arises from centriole. In the stage of prophase, the chromosomes begin to curl up and become thicker and appear thread-like. At the same time, the cytoskeleton becomes like a net of fibres extending all over the cell. This network of fibres is called the spindle and each fibre is called an astral ray.(Each centriole with its astral rays is referred to as a aster.) The centrioles move apart along the fibers of the spindle until they reach opposite sides of the cell- the position of the centrioles at opposite sides of the cell become the sides of the spindle. Finally, the nuclear membrane starts to break up.
Many cells function properly and divide mitotically even though they do not have
(d) The presence of plastid is a feature of plant cells but animal cells are devoid of them. Even then they function properly and divide mitotically similar to plant cells.
Which of the following is not a characteristic of meiosis?
(a) : Chromosome replication occurs once but meiosis has two M-phases each with its own Karyokinesis and Cytokinesis. As a result chromosome number is halved. The transition period between M-phase II (meiosis II) is short and without DNA replication. It is called interkinesis.
Microtubule depolymerizing drug such as colchicine is expected to
(a) : Colchicine is an alkaloid derived from the crocus, Colchicum autumnale. It inhibits spindle formation in cells during mitosis so that chromosomes cannot separate during anaphase, thus inducing multiple sets of chromosomes. It does not affect cytokinesis.
In a diploid cell, at which stage of cell cycle, the amount of DNA is doubled?
(d): S-phase is known as synthetic phase. In this stage replication of DNA takes place on the template of the existing DNA and thus the amount of DNA per cell doubles. If the initial amount of DNA is denoted as 2C, then it increases to 4C.
Which is the longest phase of the cell cycle?
(b): Cell cycle is divided into 2 phase. (i) Interphase (a period of preparation for cell division), (ii) M phase (the actual period of cell division). The interphase cell is metabolically quite active. Interphase is the long non dividing phase further divided into G1, S and G2. It occupies 75 to 90 % of entire cell division time.
Identify the correct matched pair.
In anaphase ll of meiosis centromeres divide and the spindle fibres pull the chromatids to opposite poles. Four groups of chromosomes are formed in the end of anaphase ll.
Calcium dependent Kinases can control
Calcium Dependent Kinases (CDKs) have the ability to control cell cycle activities during cell division.
During meiosis, the sister chromatids separate during:
Anaphase II begins with the simultaneous splitting of the centromere of each chromosome (which was holding the sister chromatids together), allowing them to move toward opposite poles of the cell.
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