Lecture 3b Flashcards
What is the Synthesis Phase or the S Phase?
The time it takes to replicate human chromosomes.
How long does the S phase usually take?
About 8 hours.
What do the chromosomes look like in G2 Phase?
After the chromosomal DNA molecules have been replicated, the resulting daughter chromosomes remain paired by cohesin.
What are daughter chromosomes?
The chromosomes that result from replication.
What is cohesin?
A protein glue that holds the daughter chromosomes together.
What phase is this cell in?
S phase
What phase is this cell in?
The G2 phase. We can see the cohesin holding the paired daughter chromosomes together.
What 2 things occur in Prophase of mitosis
1) The nuclear membrane breaks apart.
2) Proteins package the paired chromosomes into shorter and thicker rods (CONDENSATION).
What is condensation, in terms of protein involvement?
Proteins package chromosomes into shorter thicker rods.
If the nuclear membrane is breaking apart, what phase must be occurring?
Prophase of mitosis
If the daughter chromosomes are getting shorter and thicker, what phase must be occurring?
Prophase of mitosis.
If we said “a protein suitcase is being made”, what phase are we in?
Prophase of mitosis.
What 2 things occur in Metaphase of mitosis?
1) Cohesin is cleaved everywhere except at the centromere.
2) Microtubules attach to kinetochores on each side of the chromosome’s centromere. They pull until the chromosomes are aligned in a straight line.
What do microtubules attach to?
Kinetochores.
What are kinetochores?
A protein structure that acts as the “handle” of the centromere.
What is a centromere?
A larger protein/DNA structure that is in the center of the chromosome.
What is the metaphase plate?
An imaginary straight line where the microtubules align the chromosomes.
If chromosomes are aligned in a straight line, what phase must we be in?
Metaphase of mitosis.
If cohesin has been cleaved everywhere except at the centromere, what phase are we in?
Metaphase of mitosis.
What are microtubules?
Tiny protein ropes that attach to chromosomes.
What are homologous chromosomes?
The corresponding chromosomes from different parents.
What is a karyotype?
When chromosomes are lined up from largest to smallest.
What phase is this cell in?
Prophase of mitosis.
What phase is this cell in?
Metaphase of mitosis.
What is this?
A karyotype.
What are these?
Homologous chromosomes. One chromosome from each parent.
What are these?
Sex chromosomes.
What number are the sex chromosomes?
The 23rd pair in the karyotype.
What sex is X + Y ?
A bitch
What sex is X + X ?
A glorious woman.
What phase of mitosis does a karyotype typically come from and why?
Metaphase because homologous pairs are lined up.
T/F: At metaphase, cohesin only binds the daughters at the centromere.
True, the rest of cohesin has been cleaved.
What are centrosomes?
Protein structures at the edge of the cell that microtubules are attached to.
What 2 things happen in Anaphase of Mitosis?
1) The cohesin is cleaved.
2) The microtubules contract pulling the daughter chromosomes to opposite ends of the cell.
During Anaphase of Mitosis, how many chromosomes go to each end of the cell? Are they identical or different?
6 chromosomes, all genetically identical.
What are the arrows pointing to?
Centrosomes
What 2 things occur in Telophase of Mitosis?
1) Chromosomes reach their respective poles and decondense.
2) Nuclear membrane reforms to form two separate nuclei.
What occurs in Cytokinesis of Mitosis for animals?
Formation of a cleavage furrow.
What is a cleavage furrow?
An invagination between 2 forming nuclei. Basically, a BUTTCRACK!
What occurs in Cytokinesis of Mitosis in plants?
Formation of a cell plate.
T/F: In most cases, telophase is quickly followed by cytokinesis.
True.
What is pictured and what phase is this?
A cleavage furrow, thus, it is cytokinesis in animal cells.
In plant cells, how does cytokinesis occur?
A cell plate forms between the 2 sets of chromosomes and this grows until it splits the cell into 2 cells.
What is pictured and what phase is this?
A cell plate, thus, it is cytokinesis in plant cells.
What are the phases of mitosis in order?
1) Prophase
2) Metaphase
3) Anaphase
4) Telophase
5) Cytokinesis
What phase(s) are occurring here?
Telophase and Cytokinesis
After mitosis has occurred, what do we have?
Two daughter cells that are genetically identical to the mother cell.
How do we know if a cell is in the Cell Cycle?
It is dividing.
What is G0? Are many cells in this phase or no?
A cell that is not dividing. A vast majority of the cells in our body are in G0.
T/F: G0 is in the cell cycle.
False, G0 is NOT in the cell cycle.
What process allows for genetic material to be inherited by offspring?
Meiosis!
Overall, what happens in meiosis?
Haploid (1n) cells are produced from diploid (2n) cells.
In humans, what does meiosis entail?
A gamete must receive one chromosome copy from each of the 23 pairs of chromosomes.
Just like mitosis, what phase do cells undergoing meiosis start with?
The S phase.
After the S phase, what phase do cells undergoing mitosis/meiosis go to?
G2 phase.
How many stages does meiosis have? What are they?
2, Meiosis I and Meiosis II.
Describe Meiosis 1 Prophase
1) Replicated chromosomes are condensed.
2) Homologous chromosomes (sister chromatids) are glued together by a Synaptonemal Complex.
3) Crossing over occurs between the 4 chromosomes (tetrad/bivalents) attached.
4) The Synaptonemal Complex dissociates.
5) The nuclear membrane is fragmenting.
What are sister chromatids?
1/2 of the overall chromosome, both are genetically identical to each other.
What is the Synaptonemal Complex?
Proteins glue the homologous chromosomes together.
What is crossing over?
A physical exchange of chromosome pieces.
Describe Meiosis I Metaphase.
1) Bivalents/Tetrads are organized along the metaphase plate with random orientation.
2) A pair of sister chromatids is linked to one of the poles and the homologous pair is linked to the opposite pole.
How does Meiosis I Metaphase differ from Mitosis Metaphase?
In Meiosis I, pairs of sister chromatids are aligned in a double row.
In Mitosis, the chromosomes are aligned in a single row.
Describe the metaphase plate orientation in Meiosis I Metaphase?
The orientation is random with regards to the homologues. This means that they line up however.
What are Bivalents/Tetrads?
4 chromatids / 2 chromosomes attached.
What phase is this?
Meiosis I Metaphase
Describe Meiosis I Anaphase
The homologous chromosomes separate, while the sister chromatids on each chromosome are still connected.
This means the chromosomes from mom are going in one direction and the homologous dad chromosomes go in the other direction randomly.
What happens in Meiosis I Telophase and Cytokinesis?
Cleavage furrow forms.
What occurs in Meiosis II?
The sister chromatids get separated from each other. It looks just like mitosis but with half as many chromosomes.
Which of the following is spermatogenesis an example of?
Mitosis, Meiosis I, or Meiosis II.
Meiosis II. We are forming the 4 haploid daughter cells.
How does cell number ‘n’ change in spermatogenesis?
In Meiosis I, cell is 4n. After Meiosis I, cells are 2n. After Meiosis II, cells are 1n (haploid).
What are the male gametes?
Sperm.
What cell number ‘n’ are sperm cells?
1n, haploid.
What is the female gamete?
The egg!
How is oogenesis different from spermatogenesis?
The cytokinesis is asymmetric. Thus, we end up with 2 polar bodies and 1 egg cell (haploid).
What cell number ‘n’ is the egg cell?
1n, haploid.
What are the polar bodies?
Fucking useless!
What is the product of gametogenesis?
Haploid gametes.
What does meiosis produce?
Daughter cells that are not genetically identical.
The daughter cells contain only one homologous chromosome from each pair.
The daughter cells contain many different combinations of the single homologues.
What does mitotic cell division do?
Turns one cell into two genetically identical cells.
What does meiotic cell division produce?
The gametes: sperm and egg.
What phase is this?
Meiosis I Anaphase
What phase is this?
Meiosis I Telophase and Cytokinesis
What process is being shown?
Meiosis II
Which one will turn into the egg?
The big one
