Cell Division

Question 1

What are the phases of the cell cycle?

Answer 1

G1 (First Gap) -> S (Replication of DNA) -> G2 (Second Gap) -> M Phase (Mitosis)

Question 2

What is interphase of the cell?

Answer 2

G1, S and G2 Phases

Question 3

What happens in the G1 Phase?

Answer 3

Cell is metabolically active and continuously grows

Question 4

What happens in the S Phase?

Answer 4

DNA replication takes place -> each chromosome forms two sister chromatids connected at the centomere

• DNA content doubled, twice as many chromatids as chromosomes in G1 phase

Question 5

Describe the mechanism of DNA replication

Answer 5

Semiconservative mechanism -> DNA molecules with 1 parental strand and 1 daughter strand (from environment)

Question 6

What happens in the G2 Phase?

Answer 6

Cell growth continues and proteins are synthesised in preparation for M phase

Question 7

What are chromosomes and sister chromatids?

Answer 7

Chromosome -> Discrete unit of genetic material

Sister chromatid -> Copies of DNA produced after DNA replication

Question 8

What are the phases of mitosis?

Answer 8

Prophase -> Metaphase -> Anaphase -> Telephase (PMAT)

Question 9

Describe the prophase of mitosis

Answer 9

• Chromatin fibres condense to form metaphase chromosomes
• Mitotic spindle starts to form
• Nuclear envelope completely disintegrates

Question 10

What are kinetochore microtubules?

Answer 10

Binding of the microtubules of the mitotic spindle to the kinetochore protein located at the centromere of chromosomes

Question 11

Describe the metaphase stage of mitosis

Answer 11

• Metaphase chromosomes align themselves in a single file along metaphase plate
• Kinetochore microtubules attach to kinetochore at centromeres of chromosomes

Question 12

Describe the anaphase stage of mitosis

Answer 12

• Kinetochore microtubules shorten
• Sister chromatids seperate
• Non-kinetochore microtubules lengthen to elongate the cell

Question 13

Describe the telophase stage of mitosis

Answer 13

• Daughter chromosomes decondense
• Nuclear envelope reforms

Question 14

Describe the cytokinesis process

Answer 14

!Occurs during telophase!
- Formation of cleavage furrow -> constricts to seperate cells (Animal)

• Vesicles from golgi apparatus move along microtubules to the center of the cell -> coalesce to form cell plate (Plants)

Question 15

Role of Mitosis

Answer 15

• Enables growth in multicellular organisms
• Repair of worn-out or damaged tissues in the body
• Allows for unicellular organims to reproduce asexually
• Produces genetically identical cells

Question 16

What are homologous chromosomes?

Answer 16

• Chromosomes that are the same size, centromere location and banding pattern
• Same genes are located at same position, however alleles may differ

Question 17

What are haploids, diploids and polyploids?

Answer 17

• Diploid cells carry 2 sets of chromosomes -> humans cells are diploid
• Haploid cells contain one set of chromosomes -> gametes eg. egg and sperm
• Polyploids contain three or more chromosomes

Question 18

What are the phases of Meiosis?

Answer 18

Stage 1: Prophase I -> Metaphase I -> Anaphase I -> Telephase I (Involves bivalents of homologous chromosomes)

Stage 2: Prophase II -> Metaphase II -> Anaphase II -> Telephase II (Involves chromomes with two sister chromatids)

Question 19

Describe Prophase I of meiosis

Answer 19

• Homologous pairs undergo synapsis with each other to form a bivalent (verb: synapse)
• Crossing over occurs between non-sister chromatids -> occurs at the chiasma
• Nuclear envelope disintegrates

Question 20

Describe Metaphase I of Meiosis

Answer 20

• Bivalents become attached to kinetochore microtubules
• Independent assortment occurs as bivalents randomly align along the metaphase plate

Question 21

Describe Anaphase I of Meiosis

Answer 21

Kinetochore microtubules shorten, bivalents seperate to homologous chromosomes

Question 22

Describe Telophase I & Cytokinesis of Meiosis

Answer 22

• Homologous chromosomes decondense
• Nuclear envelopes reform
• Cleavage furrow forms to seperate cell into two daughter cells

Question 23

What does Meiosis I produce?

Answer 23

Two diploid daughter cells containing homologous chromosomes

Question 24

How are Meiosis II and Mitosis similar and different?

Answer 24

• Process of chromosomes seperating into sister chromatids is similar
• Four stages of Prophase, Metaphase, Anaphase and Telophase are basically identical
• Meiosis II produces 4 genetically different haploid gametes
• Mitosis produces genetically identical cell with same DNA content as parent cell

Question 25

How does Meiosis promote genetic variation?

Answer 25

1. Crossing Over in Prophase I
2. Independent Assortment in Metaphase I
3. Random fertilisation (only during fertilisation process)

Question 26

How does crossing over promote genetic variation?

Answer 26

• Results in sister chromatids becoming non identical
• Produces new combinations of alleles not present in parents
• Results in gametes with a combination of various traits

Question 27

How does independent assortment promote genetic variation?

Answer 27

• Bivalents line up randomly along metaphase plate and seperate
• Each daughter cell receives a different combination of maternal and paternal

Question 28

What is nondisjunction?

Answer 28

• Homologous chromosomes in Meiosis I or Sister chromatids in Meiosis II fail to seperate

Question 29

What is an allele?

Answer 29

The specific variant of a heritable feature that varies among individuals eg. black wing allele, speckled wing allele