All Free Biology MCQs with Answers

• A. Kinetochore
• B. Both centromere and kinetochore
• C. Centromere, kinetochore and areas adjoining centromere
• D. Centromere

Explanation: In metaphase, chromosomes consisting of two sister chromatids get arranged at the equator. Discontinuous fibers radiate out from two spindle poles and get connected to the disc-shaped structure at the surface of the centromere called kinetochores. These are known as chromosome fibers or tactile fibrils. A kinetochore is a complex protein structure that is analogous to a ring for the microtubule hook; it is the point where microtubules attach themselves to the chromosome.

• A. Metaphase -centromeres split and chromatids separate
• B. Metaphase - Chromosomes moved to spindle equator
• C. Anaphase - Centromeres split and chromatids separate and start moving away
• D. Telophase - Chromosomes move to spindle equator

Explanation: OptionB shows correct characteristics of above diagram

• A. Prophase I during meiosis
• B. Prophase II during meiosis
• C. Prophase of mitosis
• D. Telophase of mitosis

Explanation: The given figure shows crossing over i.e., exchange of segments between two homologous chromosomes. Crossing over is characteristic of meiosis and occurs during the pachytene stage of prophase I. Non-sister chromatids of homologous chromosomes exchange their segments due to chiasmata formation, during the process called crossing over. In this way reshuffling of genetic material occurs which produces recombinations.

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

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

• A. Chromocentre
• B. Chromomere
• C. Kinetochore
• D. Centriole

Explanation: The spindle is a microtubular apparatus that appears in many eukaryotic cells at the beginning of nuclear division and is responsible for the ordered separation of the chromosomes, being attached to the spindle fibres by their centromeres. Two types of spindle fibres can be distinguished as the interpolar fibre, which stretches continuously from pole to pole of the spindle; and the kinetochore fibre, which stretches from the pole to the centromere (kinetochore) of an individual chromosome. The mechanism by which the chromosomes move and the spindle fibres contract remains unclear. Cells of animals and lower plants possess centrioles, which act as organizer regions for spindle microtubule formation, but centrioles are absent from the cells of higher plants.

• A. Muscle contraction
• B. Membrane architecture
• C. Cell division
• D. DNA recognition

Explanation: Microtubules are unbranched hollow submicroscopic tubules of protein tubulin that develop on specific nucleating regions and can undergo quick growth or dissolution at their ends by assembly or disassembly of monomers. Microtubules form spindle during cell division. Centrioles help in cell division by forming spindle poles or microtubules. In animal cells, microfilaments collect in the middle region of the cell below the cell membrane. They induce the cell membrane to invaginate. In plant cells. cell plate is formed to separate the two daughter cells. Some of the spindle fibers called the interzonal microtubules are deposited around the phragmoplast. Vesicles from the Golgi apparatus are deposited and coalesce on the phragmoplast to form a cell plate.

• A. 28
• B. 32
• C. 7
• D. 14

Explanation: Mitosis is an equational division where after division each cell produces two daughter cells, therefore after 7 divisions one cell will give 128 cells in case of mitosis.

• A. Bivalent forming
• B. Tetrad
• C. Synapsis
• D. Crossing over

Explanation: Crossing over is responsible for inducing variability. It involves an exchange of equal segments of non-sister chromatids belonging to two different but homologous chromosomes. Crossing over takes place at four stranded stages. Only two of the four chromatids take part in crossing over. The other two are called non-crossovers. Zygotene is characterized by pairing of homologous chromosomes which is called synapsis. The first meiotic division which is completed at first telophase may be followed by cytokinesis giving rise to a dyad.

• A. Separation of sex chromosomes
• B. Synthesis of DNA and centromere
• C. Separation of homologous chromosomes
• D. Separation of chromatids

Explanation: Meiosis II is shorter than the typical mitotic division because of the shortening of the prophase of this division. The division maintains the number of chromosomes produced at the end of the reduction division. Hence, it is called homotypic or equational division, though it is similar to mitosis. The main function of homotypic division or meiosis II is to separate the chromatids of univalent chromosomes which differ from each other in their linkage groups due to crossing over.

• A. 2
• B. 3
• C. 4
• D. 6

Explanation: Each kinetochore gets 2 fibers in mitosis. It can be seen clearly in the figure that 2 spindle fibers attach to each kinetochore.