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Right CHOICE is (c) Meiosis

The best I can EXPLAIN: The haploid phase of life CYCLE occurs when the total chromosome number INSIDE the cell is reduced to half. It occurs by the process of meiosis. Fertilization RESTORES the diploid phase of life cycle.

Correct CHOICE is (d) Zygotene

Explanation: SYNAPSIS is the process of association of compact CHROMOSOMES after the first phase of PROPHASE I, leptotene. It occurs in the second phase KNOWN as the zygotene phase. The chromosomes pair with each other during synapsis.

The correct CHOICE is (a) Towards the POLES

The explanation: Separation of the SISTER chromatids occurs during the third stage of mitosis, known as anaphase. The centromeres of each chromatid are directed towards the poles while the arms of the chromosomes trail BEHIND them.

Correct OPTION is (c) METAPHASE

Easy explanation: The nuclear envelope starts disintegrating in the prophase PHASE of the M phase. HOWEVER, it is completely disintegrated in the metaphase stage. It is the second phase of mitosis or M phase.

The correct ANSWER is (b) False

The best I can explain: The NUCLEAR MEMBRANE reappears at the END of ANAPHASE I, during telophase I. Telophase I is also characterized by the appearance of the nucleolus, which was disintegrated during diakinesis.

The correct ANSWER is (c) 2 diploid cells

For EXPLANATION: Meiosis 1 involves one round of cell division in which the tetrad is separated into two daughter cells. Hence, from 4n of tetrad, two daughter cells each having 2n CHROMOSOMES are formed.

Right answer is (c) CENTRE of the cell

Easy explanation: The presence of a relatively inextensible cell wall PREVENTS furrowing in plant cells. The plant cells instead UNDERGO separation by cell plate formation that STARTS from the center of the plant cell.

Right choice is (a) Disc-shaped

For explanation: The kinetochore is a SMALL disc-shaped structure. They are present on centromeres, which are the PLACE of attachment of sister chromatids. The KINETOCHORES are the SITES of attachment of chromatids to the SPINDLE fibers.

The correct option is (a) Heart cells

To elaborate: MELANOCYTES, osteocytes and LIVER cells show cell division. Heart cells do not show cell division as the cells have exited the G1 or first gap phase in ORDER to enter a quiescent STAGE or the G0 phase.

Correct CHOICE is (c) Anaphase

To EXPLAIN: Anaphase is the third stage of M phase or mitosis. It succeeds metaphase, the phase during which the chromosomes align themselves along the equator of the CELL. In anaphase, they start SEPARATING towards the POLES.

Correct answer is (a) pachytene

To explain: CROSSING over takes place after tetrad or BIVALENT formation by the process of SYNAPSIS during zygotene. Hence, crossing over takes place during pachytene. Crossing over leads to GENETIC diversity.

Right answer is (b) False

To elaborate: DNA synthesis does not INCREASE the chromosome number. Only the amount of DNA in the cell increases. It doubles in quantity in ORDER to divide it equally between TWO daughter CELLS to be produced as a RESULT of mitosis.

The CORRECT answer is (c) Gametogenesis

Best explanation: Gametogenesis is the formation of GAMETES from some specialized DIPLOID cells. Since gametes are haploid, gametogenesis INVOLVES in the reduction of chromosome number by half through meiosis.

Right choice is (d) doubles

The EXPLANATION is: During S phase or synthesis phase, DNA synthesis or replication TAKES place. This is because at the end of every cell division, the cell SPLITS into two daughter cells which have equal amount of DNA. HENCE the amount of DNA doubles.

The CORRECT answer is (a) True

The best explanation: Zygotene is the second stage of PROPHASE I while pachytene is the third stage. Tetrad formation takes place during zygotene while crossing over and RECOMBINATION TAKE place during pachytene stage.

Right answer is (c) zygotene

To elaborate: CROSSING over and RECOMBINATION takes PLACE during the PACHYTENE stage of prophase I. The stage preceding this is the zygotene stage which is characterized by the formation of the synaptonemal complex.

Correct option is (d) Diakinesis

Easiest explanation: The disappearance of the nucleolus TAKES place during the last stage of prophase I, that is, diakinesis. This stage is ALSO characterized by the disintegration of the NUCLEAR MEMBRANE. It depicts transition to metaphase I.

Correct choice is (c) It results in tetravalent FORMATION

The explanation is: Synapsis is the process of chromosomal association that takes place in the zygotene STAGE of prophase I. It results in pairing of homologous CHROMOSOMES and involves synaptonemal complex formation. It results in BIVALENT formation.

The CORRECT choice is (d) Gametes have an incomplete set of chromosomes

Explanation: Fertilization involves the fusion of two gametes to PRODUCE an offspring. These gametes develop from diploid cells and are HAPLOID. However, they possess the complete set of chromosomes.

The CORRECT answer is (d) Nuclear envelope starts to disintegrate

To ELABORATE: During METAPHASE, the nuclear envelope has COMPLETELY disintegrated. The chromosomes spread out throughout the cytosol and the chromosomes lie at the equatorial plane, attached to spindle FIBERS.

Right option is (d) Microtubules

For explanation I would SAY: ASTERS are MADE out of microtubules, which are a type of cytoskeletal proteins of the cell. Asters radiate from centrosomes on the opposite poles of the cells during the M PHASE of cell DIVISION.

Correct option is (a) Sister CHROMATIDS REMAIN attached at the centromeres

To explain: During ANAPHASE I of meiosis, the homologous chromosomes are separated and the bivalent is HENCE, equally divided. It TAKES place after diakinesis, which is a part of prophase I. Sister chromatids are not separated.

The CORRECT choice is (C) Prophase

To elaborate: The CENTROSOME is located just outside the nucleus. During S phase, it undergoes replication. During prophase of M phase or mitosis, they start MOVING towards the opposite ends of the cell.

Right answer is (c) ANAPHASE II

Easy explanation: During anaphase I, the tetrad is DIVIDED and hence the homologous CHROMOSOMES are separated. However, the sister chromatids REMAIN attached to each other. During anaphase II, the sister chromatids are separated.

Correct OPTION is (c) Asters, Spindle fibers

To elaborate: The MITOTIC apparatus CONSISTS of asters and spindle fibers. Asters radiate out from the centrosomes present on the opposite POLES of the cell. They are MADE out of microtubules which are cytoskeletal proteins.

Right choice is (c) TELOPHASE

For explanation I would say: The major organelles of the cell, such as the nucleolus, the Golgi apparatus and the endoplasmic RETICULUM, are reformed after the sister CHROMATIDS have separated and migrated to the opposite poles, during telophase.

Right OPTION is (c) Towards the poles

To explain I would say: Separation of the sister CHROMATIDS occurs during the third stage of mitosis or the M phase of the CELL cycle, known as anaphase. The chromatids SEPARATE from each other and move to the opposite poles of the cell.

The correct CHOICE is (a) Centromere

The best explanation: Chromatids are ATTACHED to each other at the centromere. Kinetochores are the POINT of attachment of chromatids on the spindle fibers. CENTROSOME is a structure present outside the nucleus.

Correct answer is (d) REPLICATION takes place

To explain: Interkinesis is the period between MEIOSIS I and meiosis II. It is mostly short lived and occurs after telophase I. It is followed by prophase II. However, no DNA replication takes place during this period.

Right answer is (C) SHORTENING of microtubules

The explanation is: During anaphase, the chromatids are separated and start moving towards the poles from the metaphase PLATE. This OCCURS by the shortening of the microtubules which pulls the chromatids towards the poles.

Right option is (B) Diakinesis

Best EXPLANATION: Diakinesis is the LAST stage of prophase I of meiosis I during which the assembly of spindle fibers takes PLACE. Diakinesis is ALSO characterized by the disappearance of the X-shape of chiasmata.

The CORRECT answer is (C) DIPLOTENE

To elaborate: The synaptonemal complex is formed in the SECOND stage of prophase I, that is, zygotene stage. After crossing over takes place during pachytene stage, the complex is DISSOLVED during the diplotene stage.

The CORRECT choice is (a) S PHASE

For explanation: Centriole duplication as WELL as DNA duplication or SYNTHESIS takes place in the S phase or the synthesis phase of the cell cycle. DNA duplication does not take place in the gap phases G1, G2 and G0.

The correct option is (c) Presence of CELL WALL

To explain I would say: Animal cells undergo furrowing during cell division or cytokinesis. The FURROW DEEPENS, ultimately forming two cells. The presence of a relatively inextensible cell wall prevents furrowing in PLANT cells.

The correct answer is (a) DIPLOTENE

The EXPLANATION: Chiasmata is an X-shaped structure formed by the TETRAD. It occurs due to the tendency of the homologous CHROMOSOMES of a tetrad to move away from each other except at the center. It occurs in the diplotene stage of PROPHASE I.

Right choice is (b) False

To ELABORATE: Chromosomes decondense and LOSE their individuality during telophase of the M phase or mitosis phase of the cell CYCLE. It is the last STAGE of mitosis and is followed by cell division or CYTOKINESIS.

The correct option is (d) Telophase

To elaborate: The nuclear envelope reforms after the division of the sister chromatids and their MIGRATION to the opposite poles of the CELL. HENCE, it reforms during the last STAGE of mitosis, telophase.

The correct choice is (a) Chromosomes are distinct and clear

The explanation is: Telophase is the LAST STAGE of mitosis or the M phase of cell cycle. During telophase, the chromosomes are present at the POLES. They lose their INDIVIDUALITY and are decondensed. They cannot be CLEARLY visualized.

The CORRECT ANSWER is (c) X-shaped

To elaborate: The chiasmata is an X-shaped structure formed by the bivalents or the tetrads during prophase I of MEIOSIS I. It OCCURS due to the tendency of the homologous chromosomes of a TETRAD to move away from each other.

Correct choice is (c) Pachytene

For explanation: Bivalent or tetrad formation takes place during the zygotene STAGE of prophase I, after synapsis has occurred and HOMOLOGOUS chromosomes FORM PAIRS. HOWEVER, the bivalent is distinct only in the next stage, pachytene.

Correct option is (C) Interphase

The explanation is: Interphase or the RESTING period is not a PART of karyokinesis. Karyokinesis INVOLVES NUCLEAR division. The stages of M phase, namely, metaphase, anaphase and prophase are a part of karyokinesis.