NEET Practice Questions (MCQs) with Answers & Solutions

Mitosis is a type of cell division that occurs in both haploid and diploid cells. The main purpose of mitosis is to produce two genetically identical daughter cells from a single parent cell, maintaining the same chromosome number as the parent.

Spindle fibres are composed of proteins, specifically microtubules, which are polymers of tubulin proteins. These structures are crucial for the separation of chromosomes during cell division.

In mitosis, if cytokinesis does not occur, the cytoplasm does not divide, resulting in a cell that contains multiple nuclei. This is because the cell undergoes nuclear division (mitosis) but not cytoplasmic division (cytokinesis), leading to a multinucleated cell.

During meiosis, the genetic material is replicated only once during the S phase of interphase, before meiosis I begins. The cell then undergoes two rounds of division (meiosis I and meiosis II) without any further replication of DNA.

Crossing over is a process that occurs during prophase I of meiosis where homologous chromosomes exchange genetic material. This exchange increases genetic diversity by producing new combinations of alleles on the chromosomes.

Crossing over occurs between non-sister chromatids of homologous chromosomes. This process is crucial for genetic variation as it allows for the exchange of genetic material between homologous chromosomes. Homologous chromosomes are pairs of chromosomes that have the same structure and carry the same genes, but they come from different parents. During prophase I of meiosis, these homologous chromosomes pair up and exchange segments of their chromatids in a process known as crossing over.

During meiosis, the centromere divides only once at anaphase II. Meiosis consists of two stages: meiosis I and meiosis II. In meiosis I, homologous chromosomes are separated into two daughter cells, but the centromeres do not split. It is during anaphase II of meiosis II that the centromeres divide, allowing the sister chromatids to be pulled apart into separate daughter cells.

Pairing of homologous chromosomes occurs only during meiosis. This process is called synapsis and it happens during prophase I of meiosis I. During synapsis, homologous chromosomes come together and form tetrads, which allows for crossing over and genetic recombination to occur. This pairing is unique to meiosis and does not occur during mitosis.

In the cell cycle, the G1 phase is the first gap phase where the cell grows and synthesizes proteins and organelles but does not synthesize DNA (q). The S phase (synthesis phase) is where DNA replication occurs (p). The G2 phase is the second gap phase where the cell prepares for mitosis, and DNA synthesis stops (r). Therefore, the correct matching is: G1 phase - Synthesis of DNA does not occur (q), G2 phase - DNA synthesis stops (r), S phase - Synthesis of new DNA (p).

During anaphase, spindle fibers shorten, which helps pull the sister chromatids toward the opposite poles of the cell. This is a critical step in ensuring that each daughter cell will receive an identical set of chromosomes.