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# Cell Cycle and Cell Division

#### Multiple Choice Questions

1.

Which typical stage is known for DNA replication?

• Metaphase

• G1- phase

• S- phase

• G2- phase

C.

S- phase

S- phase or Synthesis phase is the phase of the cell cycle in which DNA is replicated. It occurs between G1 and G2 phase.

During this phase, DNA is replicated and histones are sythesized so that each chromosomes becomes two chromatids.

2.

What would be the number of chromosomes in the cells of the aleurone layer in a plant species with 8 chromosomes in its synergids?

• 16

• 24

• 32

• 8

B.

24

Synergids are two, short-lived, haploid cells lying close to the egg in nature embryosac of flowering plant ovule. While the endosperm is a triploid tissue formed after triple fusion. Thus, if the synergids have 8 chromosomes, the aleurone layer (part of endosperm) will have just triple of that of chromosomes in the synergids i.e, 24 chromosomes.

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3.

Crossing over occurs in

• zygotene

• leptotene

• pachytene

• diplotene

C.

pachytene

Crossing overie, exchange of segments between non- sister chromatids of homologous chromosome occurs in pachytene stage of Prophase- I of Meiosis- I.

4.

In meiosis division is

• Ist reductional and IInd equational

• Ist equational and IInd reductional

• both reductional

• both equational

A.

Ist reductional and IInd equational

The term 'Meiosis' was given by Farmer and Moore (1905). To study meiosis in plants, anther is the best part.

The process of meiosis involves two division of the genetic material. The first division is called reduction division or Meiosis I as it reduces the number of chromosomes from 46 chromosomes or 2n to 23 chromosomes or n.

Meiosis II is called equational division because it does not reduce chromosome numbers. A nuclear division that maintains the same ploidy level of the cell.

5.

Lampbrush chromosomes are seen in which typical stage

• mitotic anaphase

• mitotic prophase

• mitotic metaphase

• meiotic prophase

D.

meiotic prophase

Lampbrush chromosomes are a special form of chromoosme found in the growing oocytes of most animals, except mammals. They grow profusely during prophase of meiosis- I.

6.

In the hexaploid wheat, the haploid (n) and basic (x) numbers of chromosomes are

• n = 7  and x = 21

• n = 21 and x = 21

• n = 21  and x = 14

• n = 21  and x = 7

D.

n = 21  and x = 7

The basic (x) number of chromosome of hexaploid wheat is 7  and haploid (n) number is 21.

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7.

The term 'Meiosis' was given by

• Johansen

• Knoll and Ruska

• A. Flemming

• Farmer and Moore

D.

Farmer and Moore

Farmer and Moore (1905) proposed the term meiosis. Meiosis is a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cells, as in production of gametes and plant spores.

8.

Mitotic spindle have main protein

• tubulin

• myosin

• tropomyosin

• dynein

A.

tubulin

The mitotic spindle is a highly dynamic molecular machine composed of tubulin, motors and other molecules. It assembles around the chromosomes and distributes the duplicated genome to the daughter cells during mitosis

Microtubules are unbranched, hollow, sub- microscopic tubules, which form the structural material of cilia, flagella, basal bodies, centrioles and spindle apparatus. They are built up protofilaments, formed of two related proteins, $\alpha$ and $\beta$- tubulins.

9.

At what stage of the cell cycle are histone proteins synthesized in a eukaryotic cell?

• During entire prophase

• During telophase

• During S-phase

• During G2 stage of prophase

C.

During S-phase

Histone proteins are basic proteins used for the packaging of eukaryotic DNA. Both DNA and histones together comprise of chromatin, forming bulk of eukaryotic chromosomes. There are 5 major kinds of histones- H1, H2A, H2B, H3 and H4

H1 histone is used for linking neighbouring chromosomes while others are used as elements of nucleosomes structure. During S- phase of cell cycle, synthesis of histone proteins takes place as the chromosome number gets doubled to that of somatic number.

10.

Colchicine prevents the mitosis of the cells at which of the following stage?

• Anaphase

• Metaphase

• Prophase

• Interphase

B.

Metaphase

Colchicine, an alkaloid obtained from Colchincum autumnale (Liliaceae), prevents mitosis by inhibiting spindle formation through disruption of microtubules. It is a mitotic poison.