chapter 6- cell division

Question 1

what 3 phases does interphase consist of?

Answer 1

• G1
• S phase
• G2

Question 2

what happens in the G1 phase?

Answer 2

• cell grows in size
  -protein synthesis
• cell organelles made in preparation for division
  At the end of the G1 phase it checks for correct cell size, if cell has enough nutrients, DNA damage. if it fails it will enter G0 phase

Question 3

reasons a cell will enter G0 phase

Answer 3

• cell differentiation- can no longer divide as it is specialized
  -DNA damage- no longer viable, can cause mutations
  -Lymphocytes- an example of a cell that can re enter the cell cycle

Question 4

what happens in the S phase?

Answer 4

• DNA begins to replicate
• s phase begins when DNA replication starts and ends once the final chromosome has been replicated
• happens as quickly as possible due to the high risk of exposed bass being affected by harmful chemicals such as mutagens

Question 5

what happens in the G2 phase?

Answer 5

the gap between DNA synthesis and mitosis
the cell continues to grow
there is a G2 checkpoint to ensure the DNA has been replicated without damage. If it has been damaged the cell will try to fix it or apoptosis will occur.

Question 6

define mitosis

Answer 6

the process of dividing and replicating te genome

Question 7

define cytokinesis

Answer 7

the physical division of the cell

Question 8

what happens during mitosis?

Answer 8

• starts after interphase
• referred to as the M phase
  -cell growth stops

Question 9

what happens during cytokinesis?

Answer 9

• starts after the M phase
• Once the nucleus has divided into two genetically identical nuclei, the whole cell divides, and one nucleus moves into each cell to create two genetically identical daughter cells.
  -In animal cells, cytokinesis involves constriction of the cytoplasm between the two nuclei and in plant cells, a new cell wall is formed

Question 10

what are the 4 stages of mitosis?

Answer 10

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

Question 11

describe prophase

Answer 11

• Chromosomes condense and become visible under a microscope as distinct structures, each consisting of two sister chromatids joined at the centromere.
• The nuclear envelope breaks down, and the nucleolus disappears.
• Spindle fibers begin to form from the centrioles (in animal cells), which move to opposite poles of the cell. These spindle fibers extend from the centrosomes and are essential for chromosome movement.

Question 12

describe metaphase

Answer 12

• The chromosomes align along the equatorial plane (the metaphase plate) of the cell.
• Spindle fibers attach to the centromeres of the chromosomes via the kinetochores, ensuring that the chromosomes are properly aligned for separation.

Question 13

describe anaphase

Answer 13

• The sister chromatids are pulled apart toward opposite poles of the cell. This occurs when the spindle fibers shorten, separating the centromeres and dividing the chromatids.
• The chromatids are now considered individual chromosomes.
  -This stage ensures that each daughter cell will receive an identical set of chromosomes.

Question 14

describe telophase

Answer 14

• Chromosomes reach the poles and start to de-condense back into chromatin.
• The nuclear envelope reforms around each set of chromosomes, creating two new nuclei in the cell.
• The nucleolus reappears in each new nucleus.

Question 15

how can we increase genetic diversity in gametes?

Answer 15

• independent assortment
• crossing over

Question 16

describe the process of crossing over

Answer 16

• non-sister chromatids can cross over and get entangled
• these crossing over points are called the chiasmata
• the entanglement then places stress on the DNA molecules
• as a result of this a section of chromatid from one chromosomes may break and rejoin with a chromatid from another organism
• there is usually at least one or more chiasmata present in each bivalent during meiosis

Question 17

describe the process of independent assortment

Answer 17

• the production of different combinations of alleles in daughter cells
• Homologous chromosomes (chromosome pairs, one from each parent) are separated into different gametes during meiosis.
• During metaphase I, homologous chromosomes align randomly at the metaphase plate. This random alignment leads to different combinations of maternal and paternal chromosomes being distributed to the gametes.
• As a result, the alleles for genes located on different chromosomes assort independently of each other.
• The number of possible combinations of chromosomes is calculated using the formula 2n
• independent assortment during meiosis ensures genetic diversity by randomly distributing chromosomes into gametes, which is essential for evolution and variation in sexually reproducing organisms.