3.5- Cell Division

Question 1

What is chromatin

Answer 1

compact molecule formed from DNA associated with histone proteins

Question 2

Two types of chromatin

Answer 2

Euchromatin
Heterochromatin

Question 3

compare and contrast Euchromatin and Heterochromatin

Answer 3

Euchromatin
- active genes
- loosely packed
stains light due to high GC content

Heterochromatin
- inactive genes
- tightly packed
- stans darker due to high AT content

Question 4

Dynein

Answer 4

motor protein that facilitates chromosome movement away from the kinetochore region

Question 5

Kinesin

Answer 5

motor protein that facilitates chromosome movement towards the kinetochore region

Question 6

What is mitosis

Answer 6

a single nuclear division that results with two genetically identical daughter cells

Question 7

What is mitosis for

Answer 7

growth, tissue repair, reproduction

Question 8

What is meiosis

Answer 8

two nuclear divisions that result in four haploid daughter cells with half the amount of chromosomes as the parent cell

Question 9

Process of Mitosis

Answer 9

Prophase
DNA supercoils, chromatin condenses into chromosomes
nuclear membrane dissolves
centrosomes move to opposite poles
centrioles begin making spindle fibres

Metaphase
Kinetochores attach to centromeres of each chromosome
Spindle fibres attach to kinetochores
chromosomes move along spindle fibres to the middle of the cell, with movement facilitated by motor proteins (dynein + kinesin)

Anaphase
- cohesions holding sister chromatids together are removed
chromosomes move to the opposite ends of the cell as spindle fibres continue to contract

Telophase
Early: chromosomes arrive at the opposite ends of the cell
Late: DNA de-condenses, Nuclear membrane reforms, spindle fibres dissolve

Cytokinesis
- equal or unequal division of the cell’s components into the daughter cells
- occurs concurrently with telophase

Question 10

Cytokinesis in animal cells

Answer 10

Contractile proteins (actin and myosin) inside the plasma membrane pull the membrane in at the equator, forming a cleavage furrow.
When this furrow reaches the centre of the cells, they are able to

Question 11

Cytokinesis in plant cells

Answer 11

Vesicles of cellulose are transported to the centre of the cell during telophase, forming the cell plate.
This eventually connects with the existing cell’s membrane.
The components of the vesicles are released into the space between the cells, sticking them together.

Question 12

How does meiosis promote variation

Answer 12

Crossing over and recombination - Prophase 1
Random assortment- Metaphase 1
Chromosomal non-disjunction in anaphase 1/2

Question 13

What is crossing over and recombination

Answer 13

Synapsis might occur, connecting sections of homologous chromosomes
the connected chromosomes are known as a bivalent

While in synapsis, sections of the chromosomes may be swapped between the non-sister chromatids.
the crossing-over point is called a chiasma (pl. chiasmata)

This produces recombinant chromosomes (ie. with unique combinations of alleles unlike either parent chromosome).

Question 14

Random assortment

Answer 14

Occurs in Metaphase Ɪ

Homologous chromosomes line up randomly as bivalents (in pairs)
the inheritance of each bivalent is independent of another

This means different combinations of maternal and paternal chromosomes can be inherited

Question 15

chromosomal non-disjunction

Answer 15

Occurs in Anaphase Ɪ or ꞮꞮ

Chromosomes fail to separate, resulting in errors in the overall number of chromosomes within the gametes:
extra chromosome = trisomy
missing chromosome = monosomy

Question 16

Example of chromosomal non-disjunction

Answer 16

Down syndrome
trisomy 21

Question 17

What is amniocentesis

Answer 17

cells from the amniotic fluid

Question 18

What is chorionic villus sampling

Answer 18

cells from the placenta