Cell cycle, Mitosis, and Meiosis Flashcards
What happens during interphase
Gap 1 (G1) Phase:
During this stage, the cell grows and prepares for division.
It accumulates resources and replicates organelles.
Some cells may rest during G1 (called G0) until they eventually die.
For actively dividing cells, G1 leads to the next phase.
Synthesis (S) Phase:
Here, the cell focuses on copying its DNA.
Enzymes create identical copies of each chromosome.
These copies will later separate during cell division.
Synthesis happens after interphase.
Gap 2 (G2) Phase:
In this phase, the cell continues growing and prepares for mitosis.
How is cytokinesis different in plant and animal cells?
This is when the cell splits into two new cells.
In animal cells, it’s like pinching a balloon to divide it. The cell forms a “waistline” called a cleavage furrow and pinches in half.
In plant cells, it’s a bit different. Instead of pinching, plant cells build a new wall between them using something called a cell plate. It’s like adding a new brick wall to separate two rooms.
Purpose of mitosis
The purpose of mitosis allows a single cell to multiple and create more cells.
(tissues and regeneration, asexual reproduction)
Mitosis: Prophase
DNA condenses into visible chromosomes.
The nuclear envelope breaks down.
Spindle fibers (microtubules) form and attach to the centromeres of chromosomes.
Mitosis: Metaphase
Chromosomes align at the cell’s equator (the metaphase plate).
Spindle fibers attach to the centromeres of each chromosome.
Mitosis: Anaphase
Sister chromatids (identical copies of DNA) separate and move toward opposite poles of the cell.
The cell elongates as the separated chromatids are pulled apart.
Mitosis: Telophase
Chromatids reach opposite poles.
New nuclear envelopes form around each set of chromosomes.
Chromosomes de-condense back into chromatin.
MItosis: Cytokinesis (technically not part of mitosis but follows it)
Cytokinesis overlaps with anaphase and/or telophase.
In animal cells, a cleavage furrow pinches the cell membrane, dividing it into two daughter cells.
In plant cells, a cell plate forms in the middle, creating a new cell wall between the daughter cells.
Meiosis: Prophase
Chromosomes condense and become visible.
Homologous chromosomes (one from each parent) pair up.
Crossing-over occurs: Sections of DNA exchange between homologous
chromosomes, creating genetic diversity.
Meiosis: Metaphase
Homologous chromosome pairs align at the cell’s equator.
Spindle fibers attach to the centromeres.
Meiosis: Anaphase
Homologous chromosomes separate and move toward opposite poles.
Each daughter cell receives a mix of genetic material from both parents.
Meiosis: Telophase
Chromosomes reach opposite poles.
Nuclear envelopes form around each set of chromosomes.
The cell divides into two daughter cells, each with half the original chromosome number.
Meiosis II
Prophase II, Metaphase II, Anaphase II, and Telophase II:
These stages are similar to mitosis but involve haploid cells.
Sister chromatids (formed during meiosis I) separate.
The result: four haploid daughter cells, each with unique genetic combinations.
Crossing-over:
Crossing-over occurs during prophase I of meiosis I.
It involves the exchange of genetic material between homologous chromosomes.
This process increases genetic diversity by shuffling alleles from both parents.
Imagine it as a genetic mix-and-match game, where segments of DNA switch places.
How meiosis increases genetic variation
In meiosis I:
Chromosomes pair up and exchange genetic material
The cell divides into two daughter cells, each with half the chromosomes.
In meiosis II:
These daughter cells divide again to create four sex cells (sperm or eggs).
Each sex cell has a mix of genetic material from both parents.
Crossing-Over:
During meiosis I, chromosomes do a little dance called crossing over.
They swap bits of DNA, creating new combinations.
This mixing and matching make sure that no two sex cells are exactly the same.
