Short Questions and Answers
One Mark Questions with Answers
1. In meiosis I centromere
(a) divides between prophase and metaphase
(b) divides between metaphase and anaphase
(c) does not divide
(d) divides but the two daughters remain attached
Answer: (c) does not divide
2. Meiosis II is meant for
(a) separation of chromatids
(b) separation of homologous chromosomes
(c) separation of sex chromosomes
(d) synthesis of DNA
Answer: (a) separation of chromatids
3. Cells from preexisting cells is the famous saying of
Answer: (d) Virchow
4. Best stage to observe shape, size and number of chromosomes is
Answer: (b) metaphase
5. DNA or chromosome replication occurs during
Answer: (d) interphase
6. When are chromatids clearly visible in meiosis
Answer: (c) diplotene
7. Chiasmata are first seen during
Answer: (d) diplotene
8. Chromosomes separate at the time of
(a) early prophase
(b) early anaphase
(c) early telophase
(d) late prophase
Answer: (b) early anaphase
9. Nuclear envelope and nucleolus disappear at the end of
Answer: (a) prophase
10. In meiosis, centromere divides during
(a) metaphase I
(b) anaphase I
(c) anaphase II
(d) metaphase II
Answer: (c) anaphase II
11. Crossing over causes
(a) segregation of alleles
(b) re-combination of linked alleles
(c) independent assortment
(d) all the above
Answer: (b) re-combination of linked alleles
12. In synapsis the two homologous chromosomes are joined by their
(d) none of these
Answer: (c) chromomeres
13. Colchicine arrests mitosis at
Answer: (b) metaphase
14. Cytokinesis is division of
Answer: (d) cytoplasm
Two Marks Questions with Answers
1. What is mitosis?
Answer: Mitosis is that type of division in which chromosomes replicate and become equally distributed both quantitativelyi and qualitatively into two daughter nuclei so that the daughter cells come to have the same number and type of chromosomes as are present in the parent cell. It is therefore, also called equational division. Mitosis was first observed by strasburger (1817) in plant cells, Boveri and Fleming in 1879 in animal cells. The term mitosis was coined by Fleming in the year 1882. Mitosis consists of two steps karyokinesis and cytokinesis.
2. Differentiate between plant cytokinesis and animal cytokinesis.
Answer: Plant cytokinesis usually occurs by cell plate method while animal cytokinesis takes place by cleavage. In plant cytokinesis the spindle usually persists during cytokinesis while in animal cytokinins the spindle begin to degenerate soon after anaphase. In plant cytokinesis cell plate grows centrifugally whereas in animal cytokinesis cleavage progresses centripetally.
3. What is meiosis?
Answer: Meiosis is a double division which occurs in a diploid cell or nucleus and gives rise to four haploid cells or nuclei each having half the number of chromosomes as compared to the parent cell. The term mitosis was coined by Farmer and Moore in 1905. The division was first of all studied by Van, Strasburger, Sutton and Winiwater.
4. What is synapsis?
Answer: During zygotene the two homologous chromosomes get attached to each other laterally due to development of nucleoprotein between them. It is similar to nucleoprotein core present between two chromatids of a chromosome. Pairing is such that genes of the same character present on the two chromosomes come to lie exactly opposite. The process of attachment of the homologous chromosomes is known as synapsis.
5. What is colchicine?
Answer: It is an alkaloid widely used in plant breeding for doubling the chromosome number. Colchicine is extracted from the corms of Autumn Crocus. The alkaloid does not allow the formation of spindle because it prevents assembly of microtubules. It is therefore called mitotic poison. The chemical does not inhibit chromosome replication. As a result the colchicine treated meristematic cells show doubling of chromosomes.
Three Marks Questions with Answers
1. What happens in telophase?
Answer: During telophase the cytoplasmic viscosity decreases. The two chromosome groups reorganise themselves into nuclei. The chromosomes elongate and overlap one another to form chromatin. The nucleolar organiser regions of satellite chromosome produce nucleoli which may or may not fuse. Nucleoplasm collects in the area of chromatin. A nuclear envelope appears on its outside from either pieces of older nuclear envelope or endoplasmic reticulum. In this way two daughter nuclei are formed at the poles of the spindle. In the telophase the spindle fibres disappear around the poles. In animal cells the astral rays are also withdrawn. Rest of the spindle fibres persist during the cell plate method of cytokinesis but disappear where cytokinesis takes place by cleavage or constriction.
2. What are the causes of anaphasic movement?
Answer: Following are the causes of anaphasic movement
(a) Each chromosome fibre or tractile fibril consists of microtubules. The spindle is also formed of microtubules. The chromosome fibres may glide over the spindle fibres by rachet mechanism or under force developed at the poles.
(b) Anaphasic movements are caused by contraction of chromosomes fibres.
(c) Formation and expansion of interzonal fibres.
(d) Dissolution of microtubules of chromosome fibres at their ends.
3. What is equatorial plate?
Answer: During metaphase discontinuous fibres coming from the two spindle poles get connected to the two centromere surfaces of each chromosome. They are called chromosome fibres or tractile fibres. Each chromosome is attached to both the spindle poles by distinct chromosome fibres. Chromosome fibres now tighten. This brings the chromosomes on the equator of the spindle. The phenomenon of bringing the chromosomes on the equator of the spindle is called congression. On the equator the small chromosomes come to lie towards the interior while the larger ones are arranged towards the periphery. The centromeres of all the chromosomes lie on the equator while the limbs are placed variously according to their size and spatial arrangement. The centromeres of all the chromosomes form an apparent plate called metaphasic or equatorial plate.
4. Differentiate between mitosis and meiosis.
Answer: Mitosis takes place in the somatic cells while meiosis occurs either in the reproductive cells or at the time of germination of zygote. The cells undergoing mitosis may be haploid and diploid while the cells undergoing meiosis are always diploid. Mitosis is a single division which produces two cells while meiosis is a double division. It gives rise to four cells. Mitosis is comparatively simple while meiosis is quite complicated. Mitosis takes less time to complete while meiosis takes longer time to complete. The daughter nuclei or cells formed after mitosis are exactly similar to the parent one while the daughter nuclei or cells formed after meiosis are neither similar to the parent nor to one another.
5. What is the significance of meiosis I?
Answer: (a) It separates the homologous chromosomes and reduces the chromosome number to one-half. This is essential for sexual reproduction.
(b) Crossing over occurs during this division. It introduces new combinations of genes or recombinations. The recombinations result in variations.
(c) There is random distribution of paternal and maternal chromosomes into daughter cells. It is a sort of independent assortment and producers variations.
(d) Due to disturbance in disjunction, chromosomal and genomatic mutations takes place.
(e) Meiosis 1 induces the cells to form spores or gametes.