Cell Cycle and Cell Division

Question 1

Who was the cell theory put forward by?

Answer 1

Schleiden and Schwann

Question 2

Define cell cycle

Answer 2

Cell cycle is a series of events that occur repeatedly throughout the life of an organism to produce more cells of the same kind

Question 3

What are the two types of cell division in living beings?

Answer 3

1. Mitosis: division of somatic cells
2. Meiosis: Occurs in germ cells and results in gamete formation

Question 4

why is meiosis called reduction division?

Answer 4

• Meiosis is the cell division that takes place in the reproductive cells
• The daughter nuclei thus formed contain only half the number of chromosomes
• Thus, it is called reduction division

Question 5

Phases of Meiosis 1

Answer 5

Prophase 1
Metaphase 1
Anaphase 1
Telophase 1
Cytokinesis

Question 6

Phases of Meiosis 2

Answer 6

Prophase 2
Metaphase 2
Anaphase 2
Telophase 2
Cytokinesis

Question 7

Longest phase of meiosis

Answer 7

Prophase 1

Question 8

Stages of Prophase 1

Answer 8

1. Leptotene
2. Zygotene
3. Pachytene
4. Diplotene
5. Diakinesis

Lazy Zebra Pushes Dumb Donkey

Question 9

Leptotene

Answer 9

1. Condensation and coiling of chromatin fibres
2. Chromosomes are long and thick
3. One is paternal and the other is maternal
4. They are known as homologous chromosomes

Question 10

Zygotene

Answer 10

1. Pairing of homologous chromosomes (Synapsis)
2. Chromosomes become shorter and thicker
3. The paired chromosomes are called bivalents

Question 11

Pachytene

Answer 11

1. Tetrad formation between homologous chromosomes
2. Exchange of genetic material takes place which is called crossing over

Question 12

Diplotene

Answer 12

1. Nuclear membrane disappears
2. Homologous chromosomes are held together only at certain points
3. These points of contact are known as chiasmata

Question 13

Diakinesis

Answer 13

1. Chromosomes prepare themselves for metaphase 1
2. Bivalents are more distinct in this phase
3. Spindle fibres stretch towards the centre

Question 14

Prophase 1 (Briefly)

Answer 14

1. Chromosomes condense
2. Nuclear envelope breaks down
   3, Crossing over occurs

Question 15

Metaphase 1

Answer 15

Homologous chromosomes line up at the equatorial plane

Question 16

Anaphase 1

Answer 16

Homologous chromosomes move towards opposite poles of the cell

Question 17

Telophase and Cytokinesis

Answer 17

1. Chromosomes gather at the poles of the cells
2. Cytoplasm divides

Question 18

Prophase 2

Answer 18

1. Chromosomes of the daughter cells condense
2. Nuclear membrane disappears
3. Crossing over does not take place

Question 19

Metaphase 2

Answer 19

1. The chromosomes of each of the daughter cells individually align along the equatorial plane at the metaphase plate
2. Spindle fibres stretch towards the centre for this arrangement

Question 20

Anaphase 2

Answer 20

1. Chromosomes separate
2. Centromeres separate
3. Sister chromatids of each chromosome move to opposite poles along the spindle fibres
4. Spindle fibres shorten

Question 21

Telophase 2

Answer 21

1. A distinct cleavage furrow forms in each of the daughter cells
2. Nuclear membrane starts forming within each extreme of the cell

Question 22

Cytokinesis

Answer 22

1. Cleavage furrow deepens, splitting the daughter cells into two equal halves
2. Four daughter cells are formed, each having a haploid set of chromosomes

Question 23

Significance of meiosis

Answer 23

1. Meiosis forms gametes required for sexual reproduction
2. It maintains the fixed number of chromosomes in sexually reproducing organisms
3. In meiosis, maternal and paternal chromosomes assort independently, thus creating variations in traits
4. Meiosis creates genetic recombination that makes progeny have unique characteristics of their own