All Free Biology MCQs with Answers

• A. Metaphase ­- Spindle fibers attached to kinetochores, centromeres split and chromatids separate
• B. Metaphase -­ Chromosomes moved to spindle equator, chromosomes made up of two sister chromatids
• C. Anaphase ­- Centromeres split and chromatids separate and start moving away
• D. Late prophase ­- Chromosomes move to spindle equator

Explanation: Each metaphase chromosome is a duplicated structure which consists of two sister chromatids, attached at a point called centromere or primary constriction. The centromere has special area, the kinetochore, with specific base arrangement and special proteins where kinetochore fibers of mitotic apparatus attach. The kinetochore fibers of spindle attach to the kinetochore region (specialized area in centromere) of chromosome, and align them at the equator of the spindle forming equatorial plate or metaphase plate.

• A. Metaphase I
• B. Anaphase II
• C. Prophase I
• D. Prophase II

Explanation: (c) : During gamete formation, the enzyme recombinase participates during pachytene stage of prophase I. This stage is characterized by the appearance of recombination nodules, the sites at which crossing over occurs between non-­sister chromatids of the homologous chromosomes. Crossing over is the exchange of genetic material between two homologous chromosomes. Crossing over is also an enzyme­mediated process and the enzyme involved is called recombinase.

• A. Prophase I during meiosis
• B. Prophase II during meiosis
• C. Prophase of mitosis
• D. Both prophase and metaphase of mitosis

Explanation: The given figure shows crossing over i.e., exchange of segments between two homologous chromosomes. Crossing over is a characteristic of meiosis and occurs during the pachytene stage of prophase I.

• A. Metaphase I
• B. Metaphase II
• C. Anaphase I
• D. Anaphase II

Explanation: During anaphase I, from each tetrad two chromatids of a chromosome move as a unit (dyad) to one pole of a spindle, and the remaining two chromatids of its homologue migrate to the opposite pole. Thus, homologous chromosomes of each pair, rather than the chromatids of a chromosome, are separated. As a result, half of the chromosomes, which appear in early prophase, go to each pole. Thus the paternal and maternal chromosomes of each homologous pair segregate during anaphase I independently of the other chromosomes.

• A. Chromatids separate but remain in the cen­tre of the cell in anaphase.
• B. Chromatids start moving towards opposite poles in telophase.
• C. Golgi complex and endoplasmic reticulum are still visible at the end of prophase.
• D. Chromosomes move to the spindle equator and get aligned along equatorial plate in metaphase.

Explanation: (d) : The plane of alignment of the chromosomes at metaphase is referred to as the metaphase plate. The key features of metaphase are, (1) Spindle fibres attach to kinetochores of chromosomes (2) Chromosomes are moved to spindle equator and get aligned along metaphase plate through spindle fibres to both poles.

• A. Satellites
• B. Secondary constrictions
• C. Kinetochores
• D. Centromeres

Explanation: The key feature of metaphase is the attachment of spindle fibres to kinetochores of chromosomes. Kinetochores are disc­shaped structures at the surface of the centromeres. These structures serve as the sites of attachment of spindle fibres to the chromosomes that are moved into position.

• A. Late prophase
• B. Early metaphase
• C. Late metaphase
• D. Early prophase

Explanation: During early prophase of mitosis, the nucleus and cell become spheroid. The viscosity and refractivity of cytoplasm increases. DNA molecules condense to form a shortened chromosome. The endoplasmic reticulum and nucleolus start disappearing.

• A. During G2 stage of prophase
• B. During S­-phase
• C. During the entire prophase
• D. During telophase

Explanation: During the S phase or synthetic phase, the replication of DNA takes place. For replication of DNA, histone proteins are required so they are also synthesized during this phase. It takes about 30%­ 50% of the total cell cycle. Prophase and telophase are stages involved in mitosis or meiosis. During the G2 phase, the division of centrioles, mitochondria and chloroplasts occurs.

• A. In G 1 phase DNA content is double the amount of DNA present in the original cell
• B. DNA replication takes place in S phase
• C. A short interphase is followed by a long mitotic phase
• D. G2 phase follows mitotic phase

Explanation: Interphase is the stage between two successive cell divisions. During interphase, chromosomes are decondensed and are distributed throughout the nucleus. It is the largest period in the cell cycle and is divided into three phases ­ G 1 , S and G 2 . During G 1 phase the cell grows and synthesis of tRNA, mRNA, ribosomes, enzymes and proteins necessary for DNA synthesis occurs. During S phase replication of DNA takes place. The nucleotides get assembled and DNA molecules are synthesized. During G 2 phase organelles like centrioles are doubled and mitochondria, chloroplasts etc. divide.

• A. Metaphase
• B. Telophase
• C. Anaphase
• D. Late prophase

Explanation: Metaphase is the best time to count and study the number and morphology of chromosomes. The distinctly visible chromosomes arrange themselves at the equatorial or metaphasic plate. The centromeres lie at the equatorial plate while the limbs are placed variously according to their size and spiral arrangement. At prophase, the chromosomes appear thin and filamentous, forming a network. So they are not very clearly visible. At telophase, the chromosomes uncoil and lengthen and therefore are not clearly seen. Anaphase also shows chromosomes distinctly and they can be counted. But during anaphase chromatids separate and start moving towards opposite poles. So metaphase is the best stage for counting.The order of visibility of the stages of mitosis under the microscope is as follows: Metaphase > Anaphase > Prophase > Telophase