Bio 130 ch. 16 study guide Flashcards
What is a karyotype?
a photographic representation of the chromosomes from an actively dividing cell. It reveals the number, size, and form of chromosomes found within an actively dividing cell
What are the steps of karyotype?
- Sample of blood is collected and treated with drugs that stimulate cell division. (chromosomes are readily seen when they are compacted in a dividing cell) Then centrifuged.
- The cell pellet is suspended in a hypotonic solution, causing the cell to swell and the chromosomes to spread out from each other.
- Centrifuged again to concentrate the cells. The cells are suspended in a fixative, stained, and placed in a slide.
- Slide is viewed with a microscope and photographed and arranged electronically on the screen.
- For a diploid human cell, 2 complete sets of chromosomes from a single cell constitute a karyotype of that cell.
Banding patterns on chromosomes
occur from preferential binding of stains to AT rich vs GC rich DNA seq
What are the different positions of centromere?
- Metacentric: near the middle
- Submetacentric: off center
- Acrocentric: near one end
- Telocentric: at the end
What are the key phases of Cell Cycle?
Interphase (G1, S, G2)
M phase (mitosis + cytokinesis)
- Divide one cell nucleus into two nuclei
- Pairs of chromatids are separated and sorted so that each daughter cell receives 46 chromosomes.
What happens during G1 phase?
- commitment to divide
- accumulate molecular changes that eventually leads to the cell division (envt conditions and signals) -> 46 distinct chromosomes
What happens during S phase?
- each chromosome replicated to form a pair of sister chromatids -> 46 pairs of sister chromatids (total 92 chromatids)
What happens during G2 phase?
- synthesis of necessary proteins for chromosome sorting and cell division + some cell growth
Cyclin
protein responsible for advancing a cell through the phases of the cell cycle by binding to a cyclin-dependent kinase
cyclin-dependent kinases (Cdks)
A protein kinase that is active only when attached to a particular cyclin. - phosphorylates the proteins needed for the next steps.
What are the 3 checkpoints in the cell cycle?
- G1 checkpoint
- G2 checkpoint
- metaphase checkpoint
G1 checkpoint
- restriction point
- determine if conditions are favorable for cell division and if the DNA is damaged.
- G1 cyclin is made in response to sufficient nutrients and growth factors.
- G1 cyclin is degraded after the cell enters the S phase.
G2 checkpoint
- checks for DNA damage, determines if all of the DNA is replicated, and monitors the levels of proteins needed for M phase.
- Mitotic cyclin is degraded as the cell progresses through mitosis.
Metaphase checkpoint
Determines if all chromosomes are attached to the spindle apparatus.
Steps of mitosis?
- Interphase: Chromosomes have already replicated during interphase.
- Prophase: Sister chromatids condense, and the mitotic spindle starts to form. The nuclear envelope begins to dissociate into vesicles. Nucleolus is no longer visible.
- Prometaphase: The nuclear envelope has completely dissociated into vesicles, and the mitotic spindle is fully formed. Sister chromatids attach to the spindle via kinetochore microtubules.
- Metaphase: Sister chromatids align along the metaphase plate.
- Anaphase: Sister chromatids separate, and individual chromosomes move toward the poles as kinetochore microtubules shorten. Polar microtubules lengthen and push the poles against.
- Telophase and cytokinesis: chromosomes decondense, and the nuclear envelope re-forms. Cytokinesis separates the mother cell into two daughter cells, and it begins with a cleavage furrow in animal cells.
What are the steps of meiosis?
a. G1 phase prior to meiosis
Chromosomes replicate using S phase and then condense at the start of meiosis
b. Meiosis I
Homologous chromosomes separate
c. Meiosis II
Sister chromatids separate
What are the steps of meiosis I?
- Prophase I: Homologous chromosomes synapse to form bivalents and crossing over occurs. Chromosomes condense, and the nuclear envelope begins to dissociate into vesicles.
- Prometaphase I
- Metaphase I: bivalents randomly align along the metaphase plate. Each pair of sister chromatids is attached to one pole.
- Anaphase I: Homologous chromosomes separate and pairs of sister chromatids move toward the opposite poles.
- Telophase I and cytokinesis: the chromosomes decondense, and the nuclear envelope re-forms. The 2 daughter cells are separated by a cleavage furrow.
What are the steps of meiosis II?
- Prophase II: Sister chromatids condense, and the spindle starts to form. The nuclear envelope begins to dissociate into vesicles.
- Prometaphase II: The nuclear envelope completely dissociates into vesicles. Sister chromatids attach to the spindle via kinetochore microtubules.
- Metaphase II: Sister chromatids align along the metaphase plate. Each pair of sister chromatids is attached to both poles.
- Anaphase II: Sister chromatids separate, and individual chromosomes move toward the poles as kinetochore microtubules shorten. Polar microtubules lengthen and push the poles apart.
- Telophase II and cytokinesis: Chromosomes decondense, and the nuclear envelope re-forms. Cleavage furrows separate the 2 cells into 4 cells.
What are the two key events during the prophase of meiosis I?
- synapsis to form the bivalents
- Crossing over of the bivalents -> chiasma becomes visible, which is the connection at a crossover site of two chromosomes
What is the difference between the end products of mitosis and meiosis?
Mitosis produces 2 diploid daughter cells that are genetically identical, while meiosis produces 4 haploid daughter cells that are genetically different. Meiosis reduces the number of sets of chromosomes.
What is the difference between mitosis and meiosis?
- DNA replication occurs prior to Mitosis and Meiosis I, but not between meiosis I and II.
- Synapsis occurs in the prophase of meiosis I to form the bivalents, and crossing over commonly occurs due to this.
- Pair of sister chromatids is attached to kinetochore microtubules form both poles on mitosis and meiosis II, while it’s attached form just one pole for meiosis I.
- While the sister chromatids align for mitosis and meiosis II, the bivalents align for meiosis I.
- Single chromatids, now called chromosomes, move to each pole for mitosis I and meiosis II, but a pair of sister chromatids moves to each pole for meiosis I.
What is polyploidy?
organism or cell that has three or more sets of chromosomes
(ex: triploid organisms are referred to as 3n and tetraploid is 4n, and they are euploid because they have complete sets of chromosomes.)
What is aneuploidy?
alternation of the number of a particular chromosome present in an organism or cell, so the total number of chromosomes is not an exact multiple of a set.
What is nondisjunction?
event in which the chromosomes do not separate properly during cell division.
- During meiosis I: all haploid cells are aneuploids, resulting in gametes with 4 chromosomes and 2 chromosomes, instead of 3. (two of each n+1 and n-1)
- During meiosis II: two haploid cells are fine, but the other two will be each n+1 and n-1.
