Lecture 10: CSF Cell Division

Question 1

Do all cells in one human have the same DNA?

Answer 1

Yes

Question 2

How are cells different even though they contain the same DNA?

Answer 2

Different parts of DNA (genes) are expressed

Question 3

What are the 3 possible outcomes for a cell?

Answer 3

Live and function without dividing

Grow and divide

Die

Question 4

What are somatic cells?

Answer 4

Body cells (all cells excluding gametes) - diploid (2n)

Question 5

Why do somatic cells need to divide?

Answer 5

Tissue replacement

Growth

Question 6

What is mitosis?

Answer 6

The division of a diploid cell to form two identical diploid daughter cells

Question 7

What is meiosis?

Answer 7

The division of a diploid cell to form four haploid sex cells with different genetical information to parent cell

Question 8

What are the steps of the eukaryotic cell cycle?

Answer 8

Mitotic phase -> G1 phase -> S phase -> G2 phase -> mitotic phase

Question 9

What is interphase?

Answer 9

G1 phase S phase and G2 phase

Most cells of the body are performing there functions in interphase.

Question 10

What occurs in the G1 phase?

Answer 10

Most cellular activities - the duration varies from cell to cell

Question 11

What occurs in the S phase?

Answer 11

DNA replication - 23 sets of chromosomes before exist as single chromatids, they become 23 sets of chromosomes which are formed from two sister chromatids pairing up

Question 12

What occurs in the G2 phase?

Answer 12

Checks for correct DNA synthesis
Preparation for mitosis (synthesis of proteins and enzymes, gathering of reactants)
Replication of centrosomes (made up of centrioles which organise microtubules)

Question 13

What are the steps of the mitotic phase?

Answer 13

Prophase (early and late)
Metaphase
Anaphase
Telophase
Cytokinesis

Question 14

What occurs in prophase of mitosis?

Answer 14

DNA condenses (existing as two identical chromatids per chromosome - sister chromatids)
Mitotic spindle begins forming
Nuclear envelope breaks down

Question 15

What occurs in metaphase of mitosis?

Answer 15

Condensed chromosomes align at the equator via their centromeres

Question 16

What occurs in the anaphase of mitosis?

Answer 16

The microtubules contract pulling apart sister chromatids to each end of the cell

Question 17

What occurs in the telophase of mitosis?

Answer 17

Nuclear envelope reforms

Cleavage furrow

Question 18

What are diploid cells?

Answer 18

Cells with 2 sets of chromosomes

Question 19

What are haploid cells?

Answer 19

Cells with only 1 set of chromosomes (sex cells)

Question 20

At what points do checkpoints exist for the mitotic cycle?

Answer 20

At the end of G1 phase (G1 checkpoint)
At the end of G2 phase (G2 checkpoint)
At the end of metaphase during mitosis (M checkpoint)

Question 21

What is the G1 checkpoint?

Answer 21

Checkpoint near the end of G1 phase that checks for:

• Is the DNA undamaged?
• Is cell size and nutrition ok?
• Appropriate signals present?

Question 22

What happens if a cell does not pass the G1 checkpoint?

Answer 22

Enters G0

Question 23

What is the M checkpoint

Answer 23

Checkpoint at the end of metaphase to check whether all chromosomes have been attached to the equator of the spindle

Question 24

Where does meiosis occur?

Answer 24

In the gonads (testes and ovaries)

Question 25

What are the two stages of meiosis?

Answer 25

``` Meiosis I: Prophase I Metaphase I Anaphase I Telophase I ``` ``` Meiosis II: Prophase II Metaphase II Anaphase II Telophase II ```

Question 26

What occurs in meiosis I?

Answer 26

Separation of homologous chromosomes (diploid to haploid) A diploid parent cell divides forming two haploid daughter cells with non-identical genetic information

Question 27

What are homologous chromosomes

Answer 27

Homologous chromosomes are chromosomes that share the same structure and gene loci - one from female and one from male in human

Question 28

What is synapsis?

Answer 28

When two sister chromatids of each pair of homologous chromosomes pair up = two chromosomes, each with two sister chromatids paired up, that have the same structure and gene loci, pair up A 4 chromatid structure called a tetrad is formed

Question 29

What is a tetrad?

Answer 29

A 4 chromatid structure formed from synapsis in which homologous chromosomes each with 2 sister chromatids paired up pair up.

Question 30

What occurs in prophase I of meiosis?

Answer 30

Homologous chromosomes pair up Nuclear envelope breaks down Spindle begins forming Crossing over occurs - non-sister chromatids (chromatids from different chromosomes) pair up forming chiasmata and exchange genetic information

Question 31

What is chiasmata?

Answer 31

Overlap of non-sister chromatids in a homologous pair of chromosomes

Question 32

What is crossing over?

Answer 32

Exchange of genetic information between non-sister chromatids in a homologous pair of chromosomes during prophase I.

Question 33

What occurs in metaphase I of meiosis?

Answer 33

The kinetochore (at centromere) of homologous chromosomes line up at the equator of the spindle Independent assortment - the random splitting of homologous chromosomes at the equator during metaphase I

Question 34

What occurs during anaphase I of meiosis?

Answer 34

The homologous chromosomes separate | Sister chromatids remain attached

Question 35

What occurs during telophase I of meiosis?

Answer 35

Cleavage furrows

Question 36

What occurs during meiosis II?

Answer 36

Each of the 2 daughter haploid cells divide in a process identical to mitosis forming 4 daughter haploid cells

Question 37

What are the 3 sources of genetic variation and at what points do they occur?

Answer 37

Crossing over - prophase I Independent assortment - metaphase I Fertilisation - fusion between two gametes