Week 1 Flashcards
Mitosis and meiosis
What is cell division?
The process by which cells make more cells
What are the four main reasons cells divide?
- Growth
- Cell replacement
- Healing
- Reproduction
What type of cells undergo mitosis?
Stem cells
What type of cells undergo meiosis?
Sex cells
Describe the genome of eukaryotic cells
Large and linear
Where is DNA located in eukaryotes?
The nucleus
Describe the genome of prokaryotic cells
Small and circular
Where is DNA located in prokaryotes?
The cytoplasm
What are the two stages of the cell cycle?
- M phase (mitosis or meiosis)
- Interphase
What are the four stages of interphase (in order)?
- G1 phase
- S Phase
- G2 phase
- G0 phase (mitosis only)
What occurs during the G1 phase of interphase?
Growth, cellular metabolism
What occurs during the S phase of interphase?
DNA replication (chromosome duplication)
What occurs during the G2 phase of interphase?
Preparation for mitosis/meiosis
What occurs during the M phase of the cell cycle?
Chromosomal separation and cytokinesis
What is interphase?
The time between successive cell division (G1, S, G2)
What is the state of a cell when it exits the cell cycle?
G0
In what state are cells said to be quiescent?
G0
How many chromosomes are in the human genome?
46 chromosomes (23 pairs)
What are homologous chromosomes?
Pairs of chromosomes of the same type (carrying the same set of genes)
What are centromeres?
The constriction site that holds sister chromatids together
What are sister chromatids?
Two identical copies of a chromosome produced by DNA replication
What does ploidy describe?
The number of complete sets of chromosomes in a cell
What is a haploid cell?
A cell with one complete set of chromosomes
How are haploid cells denoted?
n
What is an example of a haploid cell?
A human sperm or egg cell
What is a diploid cell?
A cell with two complete sets of chromosomes (one from father, one from mother)
How are diploid cells denoted?
2n
What is an example of a diploid cell?
Somatic cells
Why are cells still considered diploid after S phase (even though there are now 4 complete sets of chromosomes)?
- The amount of DNA/chromosomes changes, but the actual type doesn’t
- It is a short and transient phase
In mitosis, the amount of _____ changes, but not the ________ ________.
DNA, ploidy level
What is a polyploid cell?
A cell with four or more complete sets of chromosomes
What are the five stages of mitosis (in order)?
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
What occurs during prophase of mitosis?
- Chromosomes condense
- Centrosomes radiate microtubules (aka mitotic spindles) and migrate to opposite poles
What occurs during prometaphase of mitosis?
- The nuclear envelope breaks down
- Microtubules of the mitotic spindle attach to the centromeres of chromosomes
What are kinetochores?
The protein complex where spindle fibres attach on each side of the centromere
What occurs during metaphase of mitosis?
Chromosomes align in the centre of the cell
What occurs during anaphase of mitosis?
Sister chromatids separate into individual chromosomes (when the centromere splits) and travel to opposite poles
What occurs during telophase of mitosis?
The nuclear envelope re-forms and chromosomes decondense
What is cytokinesis?
Occurs at the end of mitosis to create two seprate daughter cells
What is the difference between cytokinesis in plant cells and animal cells?
- Animal cells form a contractile ring and pinch apart
- Plant cells don’t pinch apart, they form a cell plate (new cell wall) and split
What is the result of a cell undergoing mitosis but not cytokinesis?
A multinucleate cell
T or F: Mitosis can continue in perpetuity
True
What is meant by saying meiosis is a terminal event?
It’s the last “step” of cell division
What is the result of the first division in meiosis (meiosis I)?
Homologous chromosomes are randomly separated
What is the result of the second division in meiosis (meiosis II)?
Sister chromatids are split
How does the end result of mitosis differ from meiosis?
- Mitosis: 2 identical daughter cells
- Meiosis: 4 unique daughter cells
What is the ploidy level of the products of mitosis?
Daughter cells are diploid (2n)
What is the ploidy level of the products of meiosis?
Daughter cells are haploid (n)
What are the stages of meiotic cell division?
- Interphase
- Meiosis I
- Meiosis II
- Meiotic division of cytoplasm
What are the stages of meiosis I?
- Prophase I
- Prometaphase I
- Metaphase I
- Anaphase I
- Telophase I and cytokinesis
What are the stages of meiosis II?
- Prophase II
- Prometaphase II
- Metaphase II
- Anaphase II
- Telophase II and cytokinesis
When does crossing over occur?
Prophase I of meiosis
What is crossing over?
When non-sister chromatids physically break and exchange maternal and paternal genetic material
In terms of cell division, what is synapsis?
The gene for gene pairing of homologous chromosomes
What are non-sister chromatids?
The chromatids (with different centromeres) that are attached in the bivalent
T or F: Non-sister chromatids are identical.
False. They carry the same set of genes in the same order, but are not genetically identical (one is maternal and one is paternal).
What is a bivalent?
The four stranded chromosomal structure composed of a pair of synapsed chromosomes (two pairs of sister chromatids aligned along their length)
What is the chiasma?
The visible manifestation of a crossover within bivalents
What are recombinant chromatids?
The result of crossing over at chiasmata between non-sister chromatids
What holds the bivalents together during while they become oriented during metaphase I?
Chiasmata
T or F: The positions of crossovers along the chromosome are random.
True
What are the main 5 things that occur during prophase I of meiosis?
- Chromosomes become visible (replication is already complete)
- Homologous chromosomes undergo synapsis
- Bivalents are formed by each pair of homologous chromosomes (when synapsis is complete)
- The chiasmata between non-sister chromatids become apparent (the result of crossing over)
- The nuclear envelope begins to break down
What occurs during prometaphase I of meiosis?
Spindles attach to kinetochores on chromosomes
What occurs during metaphase I of meiosis?
Homologous chromosomes line up in the centre of the cell
How are bivalents oriented during metaphase I of meiosis?
Bivalents are oriented randomly with respect to each other
How does kinetochore attachment differ between mitosis and meiosis I?
- Mitosis: Sister kinetochores are attached to opposite sides of the chromosome
- Meiosis I: The kinetochores orient side by side on one side of the chromosome (mono orientation)
What occurs during anaphase I of meiosis?
Homologous chromosomes separate, but sister chromatids do not
What occurs during telophase I and cytokinesis of meiosis?
- A nuclear envelope briefly reappears
- Cytoplasm divides and two separate cells are formed
What is the ploidy level of cells after cytokinesis of meiosis I?
The two daughter cells are haploid (n) because both the amount and type of DNA have been reduced
What occurs during prophase II of meiosis?
The nuclear envelope breaks down and the chromosomes condense
What occurs during prometaphase II of meiosis?
Spindles attach to kinetochores on chromosomes
What occurs during metaphase II of meiosis?
Chromosomes align in the centre of the cell
What occurs during anaphase II of meiosis?
Sister chromatids separate
What occurs during telophase II and cytokinesis of meiosis?
The nuclear envelope re-forms and the cytoplasm divides
T or F: In multicellular organisms, division of cytoplasm during meiotic cell division differs between sexes
True.
How does cytoplasm divide among female cells undergoing meiosis?
- Meiosis I: Cytoplasm divides unequally, resulting in one oocyte and one polar body
- Meiosis II: Cytoplasm of oocyte divides unequally, resulting in one functional ovum (after maturation) and another polar body (polar body from meiosis I also divides and creates two polar bodies)
What are the final products of meiotic division of cytoplasm in female mammals?
One oocyte and three polar bodies
How does cytoplasm divide among male cells undergoing meiosis?
Cytoplasm divides equally in both meiotic divisions, resulting in four unique sperm cells