31 Years NEET Previous Year Questions: Cell Cycle & Cell Division - 1 - NEET MCQ

Anaphase II: It 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 by shortening of microtubules attached to kinetochores.

G₁ Phase is metabolically active stage of cell cycle. Different type of amino acid RNA, Protein synthesis take place in G₁ phase but DNA replication does not take place, (Note :- DNA replication occur in S-Phase)

Cells in the G0 phase have exited the cell cycle and are not actively dividing. However, they are still metabolically active and capable of responding to stimuli that can cause them to reenter the cell cycle and divide. The G0 phase is also referred to as the "quiescent phase," as the cells are in a state of relative rest or quiescence. Cells in the G0 phase may be found in tissues that do not require frequent cell division, such as fully developed organs, or in cells that have undergone cellular senescence and are no longer able to divide. The G0 phase is a normal part of the cell cycle and is not necessarily a terminal phase; cells can return to the G1 phase and reenter the cell cycle if the appropriate signals are received.

During diplotene, the nucleoprotein fusion complex of synapsed chromosomes dissolves partially therefore homologous chromosomes separate except in the region of crossing over.

Mitosis is divided into four phase prophase, metaphase, anaphase and telophase. During prophase, the indistinct and intertwined DNA molecule condenses to form elongated chromosomes. The nuclear membrane disintegrates during prometaphase During metaphase, the chromosomes align themselves at the equatorial plate. During anaphase, centromere of each chromosome divides into two so that each chromosome come to have its own centromere Chromatids move towards opposite poles along the path of their chromosome fibres. Finally, during telophase, two chromosome groups reorganise to form two nuclei. Nuclear envelope reappears, Golgi complex and endoplasmic reticulum are reformed Crossing over occurs during meiosis.
Option (c) also gives the correct sequence of event but it misses step II (nuclear membrane disassembly). Hence, is ruled out as best appropriate answer is option (a).

In schematic break­up of the phases/ stages of cell cycle, D synthetic phase is the correct indicat

In meiosis I, the starting cell is diploid, and it produces 2 haploid daughter cells. Since the number of chromosomes was halved, it is a reductional division. Note that while each of the daughter cells is haploid, each of the chromosomes in the daughter cells consists of 2 sister chromatids joined together.

In meiosis II, the starting cells are haploid, and each one produces 2 haploid daughter cells. Since the number of chromosomes remained the same, it is an equational division.

Segregation of Mendelian factor (Aa) occurs during Anaphase-I. During Anaphase-I chromosome divides at the point of centromere or kinetochore and thus two sister chromatids are formed, which are called as chromosomes.

Mitotic anaphase differs from metaphase in possessing same number of chromosomes and half number of chromatids. During anaphase of mitosis, chromosomes divide at the point of centromere or kinetochore and thus two sister chromatids are formed which are called as chromosomes. While during metaphase, chromosomes become maximally distinct due to further contraction and thus size of chromosomes is measured at mitotic metaphase.

Due to segregation, independent assortment and crossing over at the time of meiosis, daughter cells exhibit variation.

In meiosis I, synapsis formation occurs in the zygotene stage of prophase-I. It is the second stage of prophase-I. During this stage, the chromosomes start pairing together and this process of association called synapsis. Such paired chromosomes are called homologous chromosomes. This synapsis is accompanied by the formation of synaptonemal complex formed by bivalent or tetrad chromosomes. 

Meiosis II is homotypic division specially for maintanence of the haploid number, separating the chromatids from each other in a chromosome.

During metaphase, the centomeres of the chromosome lie on the equatorial plate according to their size and spatial arrangement. So it is the best time to count the number and study the morphology of chromosomes.

Meiosis provides a chance for new combinations of chromosomes mainly by the phenomenon of crossing over and random distribution of homologous chromosomes between daughter cells.

The points of attachment between homologous chromosomes after their separation in diplotene are called  chiasmata. The process of pairing of homologous chromosomes is called synapsis the phenomenon by which DNA isolated from one type of cell, when introduced into another type, is able to bestow some of the properties of the former to the latter is known as transformation.

G1 phase, also called Gap I phase is characterized by increase in cell size. In the S phase or synthetic phase DNA molecules replicate. G2 is the second growth phase. Gap II where in there is intensive formation of RNAs and  proteins. In the mitotic metaphase, the chromosomes are arranged at the equatorial plate.

Lampbrush chromosomes are highly elongated bivalent chromosomes of diplotene stage, which are held together by chiasmata and  have a large number of lateral loops for rapid transcription.

Colchicine is a mitotic poison which inhibits the appearance of spindle fibres.

Plants cells do not have centrioles. Cell plate appears during cytokinesis in dividing cells. Centromere holds the sister chromatids in a chromosome. Spindle fibres appear during metaphase.

Seven mitotic divisions are required to form 128 cells from a single cell. If we start with one cell and it doubles after one round, we have 2 cells. Those 2 cells double to form 4 cells, then those 4 cells double to form 8. The math continues until we reach 128 cells.

Metaphase in characterized by the appearance of spindle fibres. Anaphase involves movement of chromatids towards the poles. Cytokinesis marks the division of the cytoplasm of the parent cell into daughter cells.

The nuclear membrane is present at prophase, when the cell moves from prophase it disappers and again it reappears in telophase.

The spindle fibres involved in cell division is made of microtubules

Kinetochore is the proteinaceous covering of centriole, to which spindle fibers attach.

Root tip is the part of the plant which grows continuously as it search water and nutrients. Thats why we can use the root tip for the study of mitosis in a laboratory easily.

Colchicine inhibits spindle formation, due to which chromatids are unable to separate during anaphase which results in doubling of chromosomes. So, if a diploid cell is treated with colchicine, there is doubling of chromosomes and it becomes tetraploid,. Its an alkaloid obtained from Colchicum autumnale.

DNA replication is restricted to S­ phase of interphase.  G2 phase is followed by the mitotic phase which is shorter than the inter phase.  In G2  phase DNA content is double than the amount present in the original cell.

Chromosomes are most distinct  in the metaphase stage. In the telophase stage they  regain their  coiled composition. In anaphase the chromatids separate and move towards opposite poles. In prophase stage the chromosomes appear thread like and individual chromatids cannot be seen.

At telophase stage, nuclear membrane vesicles associate with the surface of individual chromosomes and fuse to reform the nuclear membranes, which partially enclose clusters of chromosomes before coalescing to reform the complete nuclear envelope. During this process the nuclear pores reassemble and   (the dephosphorylated reassociare to form the nuclear lamina.) One of the lamina proteins (lamina - B) remains with the nuclear membrane fragments throughout mitosis and may help nucleate ressembly. After the nucleus reforms, the pores pump in nuclear proteins, the chromosome decondense and RNA synthesis causing the nucleolus to reappear.

Histone proteins are synthesized during S­phase of cell cycle. S­phase or Synthetic phase.

 Histone proteins are basic proteins and are used in packing of eukaryotic (absent in prokaryotes) DNA. DNA and histones together comprise chromatin, forming bulk of the eukaryotic chromosomes. Histones are of five major kinds 

H1,H2A,H2B,H3

 and 

H4H1

 histones link neighbouring nucleosomes (fundamental packing units of an eukaryotic chromosome), while other are elements of nucleosome structure. During S-phase of cell cycle synthesis of histone proteins take place because at this stage number of chromosomes become double to that of somatic number