chapter 6- cell division Flashcards
what 3 phases does interphase consist of?
- G1
- S phase
- G2
what happens in the G1 phase?
- 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
reasons a cell will enter G0 phase
- 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
what happens in the S phase?
- 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
what happens in the G2 phase?
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.
define mitosis
the process of dividing and replicating te genome
define cytokinesis
the physical division of the cell
what happens during mitosis?
- starts after interphase
- referred to as the M phase
-cell growth stops
what happens during cytokinesis?
- 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
what are the 4 stages of mitosis?
- prophase
- metaphase
- anaphase
- telophase
describe prophase
- 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.
describe metaphase
- 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.
describe anaphase
- 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.
describe telophase
- 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.
how can we increase genetic diversity in gametes?
- independent assortment
- crossing over
describe the process of crossing over
- 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
describe the process of independent assortment
- 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.
what is an organ system?
a group of organs working together to perform an essential function
what is cambium?
Cambium tissue is the layer of cells in a plant that provides unspecialized cells to promote growth.
outline the ways in genetic variation is produced.
- independent assortment (in meiosis)
- crossing over (in meiosis)
- mutations
- DNA checks during replication did not recognise damage
- Random fusion of gametes during fertilization produces genetically unique offspring
-The movement of alleles between populations due to migration.
explain why meiosis needs to have twice as many stages as mitosis (3)
- to halve chromosome number/ reduce from 2N to N.
- to separate homologous pairs of chromosomes and sister chromatids
- because DNA was previously replicated
what feature of the DNA molecule is changed as a result of mutation? (1)
the sequence of bases
what are two examples of specialized plant cells?
- palisade cells
- guard cells
what is an organ system?
multiple organs working together to carry out an overall function