MItosis

Question 1

Define mitosis

Answer 1

• type of nuclear division
• production of 2 daughter nuclei, genetically identical to parent
• same no. of chromosomes as parent nucleus

Question 2

Chromosomes

Answer 2

• rod-like structure
• visible in nucleus during cell division
• contains 1 DNA molecule that is highly coiled and condensed arnd histones
• carries genes

Question 3

Homologous chromosomes

Answer 3

• exist pairs, one paternal, one maternal
• same gene loci, centromere position, length
• diff alleles

Question 4

Gene

Answer 4

• segment of DNA in a chromosome
• where specific genetic (hereditary) info is stored
• controls production of specific polypeptide/specific protein

Question 5

Alleles

Answer 5

• diff forms of same gene
• occupy same relative positions on a pair homologous chromosome
• letters used to represent alleles

Question 6

The cell cycle

Answer 6

• sequence of events frm when cell is formed till its division in to 2 daughter cells
• 3 stages
• interphase( resting stage), mitosis (nuclear division), cytokinesis (division of cytoplasm)

Question 7

Interphase

Answer 7

• resting/non-dividing stage
• cells absorb nutrients
• build up protoplasm
• synthesis new organelles
• replicate DNA

Question 8

What happens in interphase

Answer 8

• chromosomes appear as chromatin threads
• chromatin threads replicate
• centrioles replicate and divide (animal cells)

Question 9

Why must DNA replication and mitosis be precisely controlled

Answer 9

• ensures all daughter cells are genetically stable
• error during replication, new DNA formed diff frm original
• known as gene mutation and is passed to daughter cell
• gene mutation lead to uncontrolled division of cells (cancer), may be fatal

Question 10

Stages of mitosis (PMAT)

Answer 10

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

Question 11

Early prophase

Answer 11

• in animal cell, asters (short microtubules that grow out from centrioles) form arnd centrioles
• 2 pairs of centrioles move apart to opp poles of cell
• nucleolus disappears
• chromatin condense, coil and shorten to become chromosomes
• each chromosome, 2 sis chromatids attached to centromere (x-shaped)

Question 12

DNA replication

Answer 12

• chromatin threads replicate to produce 2 identical chromatin threads
• chromatin threads coil and shorten to form chromosomes
• each chromosome have 2 genetically identical DNA molecules (sis chromatids)

Question 13

Late prophase

Answer 13

• nuclear envelope breaks down

- spindle forms with spindle fibres, extending from one pole of cell to the other

Question 14

Metaphase

Answer 14

• line up singly along equator of spindle
• spindle fibre attached to centromere
• spindle fibres help to align chromosomes

Question 15

Anaphase

Answer 15

• each centromere divides
• spindle fibres shorten pull sis chromatids to opp poles of the cell
• once sis chromatids are separated, known as sis chromosomes

Question 16

Telophase

Answer 16

• spindle fibres disintegrates
• nuclear envelope form arnd each set of chromosomes
• a nucleolus forms inside each nucleus
• chromosomes uncoil and lengthen into thread-like structures (chromatin)

Question 17

Cytokinesis

Answer 17

• division of cytoplasm

- animal cells: furrows form, deepen and eventually divide cell into 2

Question 18

Mitosis in plants

Answer 18

• centrioles absent
• cleavage of cytoplasm dont occur,
• cell plate form between 2 daughter nuclei (by fusion of fluid filled vesicles)

Question 19

Mitosis in animals

Answer 19

• centrioles present

- cleavage of cytoplasm occur during cytokinesis (formation of furrows)

Question 20

Why is mitosis important?

Answer 20

• growth
• repair of worn-out parts of tissue, wound healing, replacement of dead cells
• asexual reproduction in plants ie. development of shoots and roots in storage organs