mitosis

Question 1

what is mitosis?

Answer 1

formation of two identical daughter cell by the division of one parent cells. daughter cell has the same number of chromosomes as the parent cell

Question 2

who discover mitosis in plants and animals?

Answer 2

plants: Stasburger

animals :Walter Flemming

Question 3

occurrences of mitosis?

Answer 3

stomatic / body cells - animal

merismatic cell - plants

Question 4

mechanisms of mitosis?

Answer 4

1) karyokinesis

2) cytokinesis

Question 5

what are the four phases under karyokinesis?

Answer 5

1) prophase
2) metaphase
3) anaphase
4) telophase

Question 6

explain prophase.

Answer 6

1) chromatin condenses to form two coiled sister chromatids. chromatids are joined by the centromere, their end is not clearly visible at this stage this stage is called spireme stage
2) centrosomes move towards the poles radiate microtubules called aster. aster along with spindle fibres for mitotic apparatus
3) at end of prophase ER, nucleolus, the Golgi body and nuclear membrane dissolves

Question 7

explain metaphase.

Answer 7

1) nuclear envelop dissolves
2) equatorial / metaphasic plate forms at the centre
3) chromatids are thickest and shortest at this stage is easy to study their morphology
- mitotic spindle formation is complete

4) chromosomes are brought towards the metaphasic plate - congression
5) chromosomes align themselves on the metaphasic plate
6) chromosomal fibres attach to the kinetochores

Question 8

what is kinetochore?

Answer 8

the disc-shaped structure around the centromere.

Question 9

what is the chromosome to chromosomal fibre ratio?

Answer 9

1:2

Question 10

explain Anaphase.

Answer 10

1) spindle fibres shortens, centrosomere splits and the chromosomes of the future daughter cell migrates toward the poles.
2) formation of inter-zonal fibres occur
3) this is the best stage to study the shape of chromosome - V, L, J, I

Question 11

what are inter zonal fibres?

Answer 11

Fibres that are present between centromeres of separating.

Question 12

explain Telophase.

Answer 12

1) sister chromatids reach the poles
2) decondensation of chromatids(uncoiling)
3) spindle fibres disappears
4) ER, nucleolus, nuclear membrane, Golgi body reappears.
5) nuclear envelope develops and covers the chromatin cluster at the poles forming two daughter nuclei.

Question 13

how does cytokinesis occur in animals?

Answer 13

1) cleavage furrow
2) centric
3) Amphiastral
4) cytokinesis occur from outside to inside - centripetal

Question 14

how does cytokinesis occur in plants?

Answer 14

1) formation of the cell plate in the middle of the cell
2) Acentric
3) Astral
4) cytokinesis occur from inside to outside - Centrifugal

Question 15

how is a cell plate formed?

Answer 15

the phragmoplast is formed by the Golgi body which centrifugally forms the cell plate

Question 16

what the significances of mitosis?

Answer 16

1) maintenance of chromosomal number - genetic stability
2) healing and regeneration
3) repair
4) maintenance of shape
5) growth
6) reproduction

Question 17

what is the formulae for the no. of mitotic divisions for “n” no. of cells?

Answer 17

n-1

Question 18

what is the formulae for the no. of generations(n) required for “Y” no. of cells?

Answer 18

Y=2^n 
eg: for 4 cells
--> 2^n = 4
    therefore n = 2
thus no. of generations required to form 4 cells is 2

Question 19

why is mitosis called equational division?

Answer 19

maintains equal no. of chromosomes.

Question 20

when is the increase in the number of chromosomes first observed?

Answer 20

anaphase