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The CORRECT answer is (b) 2

To ELABORATE: The number of cells formed at the end of the entire process of MEIOSIS is 4, but only meiosis 2 produces 2 cells. Two such events of meiosis 2 on meiosis 1 end PRODUCT ULTIMATELY gives 4 cells.

Correct ANSWER is (B) Pachytene

The explanation: Pachytene STAGE of prophase 1 is the LONGEST stage for spermatogenesis, which includes crossing over. It is a vital stage that leads to an increase in variability.

Correct CHOICE is (d) Equatorial positioning of chromosomes

To EXPLAIN I would say: Unlike mitosis in meiosis there is both DNA synthesis and HISTONE synthesis for PROTEIN compaction in meiosis stage. However, equatorial positioning is seen in metaphase only.

Right CHOICE is (d) Pairing between more than 2 chromosomes

The best I can EXPLAIN: Translocation may result in the chromosome that is partially HOMOLOGOUS to two DIFFERENT chromosomes, this result in pairing of 4 chromosomes. Also homologous segments in non-homologous chromosomes can par. But pairing with more than 2 chromosomes in a normal instance is not seen.

Right choice is (d) FEMALE Drosophila

The best I can explain: Achiasmatic meiosis has been REPORTED in males of HIGHER Diptera, Panorpa (SCORPION fly), some grasshoppers and scorpions. It is also seen during OOGENESIS in Copepoda and Lepidoptera. However, female drosophila show recombination, hence chiasma.

Correct option is (c) 3

For EXPLANATION I would say: There are 3 synaptonemal complexes, ONE central filament and 2 lateral filaments. The LC COMPLEX holds the central filament in LINE with lateral.

Right option is (a) True

To explain I WOULD say: This is stated in the retardation theory that the CHROMOSOMAL PAIRING process is quite slow. Then the RELICS uncoil that leads to proper point to point pairing of each GENE.

Correct option is (a) SYNAPSIS

To ELABORATE: The main process taking PLACE in ZYGOTENE is synapsis i.e. lengthwise PAIRING of homologous chromosome. Recombination follows this pairing and occurs in the pachytene stage.

Right OPTION is (c) Mad2

The best explanation: Mad2 is responsible for signalling improper binding of the SPINDLE FIBER to the centromere. This negative signal PREVENTS apoptosis. Mdm2 is linked to p53 while Mcm activates ORC. Mek is a part of monomeric G protein signaling.

Right option is (C) Marked increase in nuclear volume

The explanation: There is a marked increase in nuclear volume in pre-leptotene. Then the chromosomes are THIN and RANDOMLY disperses, it is the PREPARATORY STAGE for a cell to enter meiosis.

Right answer is (c) Folded, straight

Best explanation: The HEAD of the zygosome is folded while the tail is straight. The sygosomes from OPPOSITE B POINTS INTERACT with each other via this tail PORTION.

Right answer is (d) The synaptonemal complex breaks down

The explanation: In the diplotene stage the CHROMOSOMES repel each other and synaptonemal complex breaks down. REPULSION can’t be due to OPPOSITE charge but like charge, also they don’t SEPARATE completely but are JOINED at the crossing over sites which gradually terminalize.

Correct option is (a) True

Easiest EXPLANATION: This elongated DIPLOTENE of MEIOSIS 1 is known as dictyotene. The oocytes persist in this STAGE for prolonged duration TILL they are fertilized.

Right OPTION is (c) The CHROMOSOME number is reduced

For explanation I would say: In meiosis 2 the chromosome number remains the same as this is not a reduction division. The meiosis 1 was the reduction division. Karyokinesis is followed by cytokinesis and the anaphase like MITOTIC anaphase has chromosomes SEPARATING starting at the centromere.

The CORRECT CHOICE is (b) Mangifera

The explanation is: Mangifera or mango is a dicot. Most animals like canines or us human beings don’t have telophase 1. MONOCOT PLANT TRILLIUM also lacks telophase 1.

The CORRECT option is (d) 0.4%

The explanation is: Very less amount of DNA is REPLICATED during zygotene while most are replicated in S phase. This unreplicated in DNA in chromosomes HELPS to hold the chromosomes TOGETHER after zygotene.

Right choice is (d) Between THREE chromatids

The best I can explain: Crossing over can occur between TWO non-sister chromatids as well as for recombinational purpose. Crossing over also occurs between sister chromatids but it is of LESS significance as they have same genetic constitution. Three chromatids single cross over is not POSSIBLE.

Right answer is (b) False

To explain: The crossing over TAKES place at pachytene stage while the chiasma forms later. The chiasma is physical MANIFESTATION of the point of crossing over so it OCCURS after crossing over is COMPLETE.

The CORRECT ANSWER is (C) Actin

For explanation I would say: Actin is a cytoskeletal element that doesn’t participate in the syanptomenal complex formation. However, the other PROTEINS mentioned and more MAY be present.

The CORRECT OPTION is (b) 10 NM

Easiest explanation: The 10 nm fibers of synaptonemal complex are responsible for the pairing of HOMOLOGOUS chromosomes during meiosis.

The correct CHOICE is (a) Electrostatic

The EXPLANATION: Darlington has SHOWN that an electrostatic repulsive force acts between two pairs of CHROMATIDS. This LEADS to terminalization.

The correct ANSWER is (a) True

The best explanation: The carrying over of the phenomenon of DNA replication to the next stage of MEIOSIS suggests that these SITES are PROBABLY the LOCATIONS where crossing over will occur.

Right answer is (d) PROTEIN FUNCTION

Easy EXPLANATION: The rate of protein production and its turnover rate MAY be RELATED to polyribosomes but the function of a protein is specific to the protein itself. Protein function is not directly affected.

Right choice is (B) False

Best explanation: Lillium is an EXCEPTIONAL case among plants where it has a Bouquet LIKE an ARRANGEMENT of the chromosomes as seen in ANIMALS.

Right option is (c) Longitudinal double nature of chromosome starts to appear

Best explanation: In leptotene PHASE the chromosomes have BEAD on string appearance with the chromatin fiber arranged like LATERAL loops on axis. But the bivalent nature is not yet visible at that TIME.

The correct answer is (B) Many, few

For EXPLANATION: During the LEPTOTENE phase as the polyribosomes are synthesized, there are many polyribosomes ready for TRANSCRIPTION. But there are only a few ER vesicles.

Right answer is (B) The sister chromatids of the bivalent is visible

Best explanation: Telophase 1 is LIKE a resting stop before meiosis 2, it is of rather SHORT duration. The chromosomes remain compacted and the NUCLEAR membrane is reformed. It is true that the chromosomes UNLIKE mitosis are bivalent.

Correct answer is (a) 6

Easiest explanation: 24 chromatids means there are 12 CHROMOSMES. Anaphase 1 is REDUCTION division so each homologue should move to OPPOSITE pole, resulting in reduction. Finally thus there will be only 6 chromosomes at each pole.

The correct option is (d) Congression

Easiest explanation: The TWO homologous CHROMOSOMES line up ALONG the equatorial plate by the MOVEMENT of congression. The two chromosomes here behave as 1 UNIT.

Correct choice is (B) The A point pairs with ADJACENT A of other CHROMATID

To ELABORATE: The A point of the synapomere pairs with the A of adjacent synaptomere not chromatid. Only the B is connected to the other chromatid.

The correct answer is (b) The chromosomes can’t relax and are compacted

To explain: In telophase 1 the chromosomes relax EVEN when compacted. The telophase MAY be absent in most ANIMALS and the CELLS do move into a diffuse interphase. The nuclear membrane is reformed only to disappear again at meiosis 2.

Right OPTION is (d) Each homologue reaches opposite pole

The BEST EXPLANATION: In anaphase 1 it is true that the homologous move to opposite pole. The result of meiosis is ultimately 4 cells but not by 1 division. The chromatids don’t separate; centromere still binds the chromatids rather the chromosome separates at the CHIASMA interactions.

The CORRECT CHOICE is (b) False

Best EXPLANATION: In meiosis 1 the metaphase CHROMOSOMES are still attached by the chiasma. When the spindle contracts chiasma association is broken to pull the chromosomes to OPPOSITE pole.

Correct answer is (d) Centromere

The best EXPLANATION: The SEPARATION of the chromosomes in DIPLOTENE stage starts at the centromere and then PROCEEDS towards the telomere. This PROCESS is called terminalization.

Correct ANSWER is (B) Recombination nodule

To EXPLAIN I would SAY: The recombination nodule is a multienzyme complex that is responsible for recombination of two chromatids. This appears as the electron dense region between two chromatids.

The correct ANSWER is (d) The lateral filaments are connected by LONGITUDINAL connections

Easiest explanation: The two lateral elements have chromatids, i.e. they have DNA along with RNA and proteins. They are however connected via transverse elements or LC elements making a ladder LIKE an ARRANGEMENT.

Right choice is (c) TURBULENCE factor

Explanation: There is no turbulence factor LEADING to pairing in prophase, however it is true that the un-replicated DNA helps in pairing. ALSO PRECOCITY THEORY and retardation theory comes into play.

Right OPTION is (a) True

To explain: The polar ARRANGEMENT of the chromosome is a characteristic of the LEPTOTENE and ZYGOTENE stage. It is generally SEEN to disappear in the pachytene.

The correct OPTION is (d) Nucleolus remains ATTACHED to PARTICULAR tetrad

For explanation I WOULD say: During PACHYTENE stage the nucleolus is not all together broken down. It remains attached to a particular tetrad.

Correct choice is (C) There EXISTS attraction between the homologous

To explain I WOULD say: Although the homologous CHROMOSOMES are bound at the chiasma, their centromeres REPEL each other which assist separation to opposite pole.

The correct choice is (C) Diplotene

To EXPLAIN: In the diplonema stage the SC is disintegrated from all points other than crossing over points. This LEADS to terminalization.