Lecture 26: Meiosis And Fertilization Flashcards
What are the 5 phases of mitosis?
Prophase Prometaphase Metaphase Anaphase Telophase
What aspect of the cytoskeleton is essential for proper segregation of chromosomes?
Microtubules, including their motor proteins
What aspect of the cytoskeleton is required for the actual division of one cell into 2 daughter cells following mitosis?
Actin
What protein is important in mitosis and meiosis to compact the chromosomes so that they are not tangled and easier to separate?
Condensin
When does DNA replication take place?
S phase of interphase
What is the purpose of the centrosome cycle?
Duplication of centrosomes
What forms the two poles of the mitotic spindle?
Centrosomes
Duplication of the centrosomes takes place at the same time as what?
DNA replication (via G1/S-Cdk and S-Cdk)
If you are looking through a microscope at a cell and you notice:
- a distinct nucleus
- chromosomes that are not condensed
- twice as much DNA
What phase of the cell cycle is occurring?
G2 of interphase
If you are looking through a microscope at a cell and you notice:
- centrosomes
- distinction of individual chromosomes
- distinct nuclear envelope
What phase of the cell cycle is occurring?
Prophase
What protein holds the chromosomes together along their length?
Cohesin
When does mitotic spindle assembly first occur?
Prophase
Which type of microtubules are considered non-kinetochore microtubules?
Interpolar microtubules
What distinguishes kinetochore microtubules from interpolar microtubules?
They bind to the chromosomes themselves
What motor protein is most important in establishing the mitotic spindle, and which way does it move?
Kinesin - moves toward plus end
Dynein is directed toward the _________ end and it moves toward the _______ of the cell
Minus; center
During mitotic spindle assembly, what phosphorylates microtubule-associated proteins, thus contributing to dynamic instability?
M-Cdk
What stabilizes interpolar microtubules?
Crosslinking of motor proteins - Kinesins and Dynein
If you are looking through a microscope at a cell and you notice:
- no more nuclear membrane
- condensed chromosomes
- chromosomes easily distinguished
- mitotic spindle well established at poles of cell
What part of the cell cycle is occurring?
Prometaphase
What signals the sister kinetochores that they are attached correctly?
Tension generated by binding at each side, each microtubule needs to feel some resistance coming from the other side
When the chromosomes are pulled toward the poles, is this the plus or minus direction?
Minus
True or false: motor proteins and chromosomes cannot direct the assembly of a functional spindle in the absence of centrosomes
False, they can!
______ motors anchored in the cell membrane pull on astral microtubules
Dynein
If you are looking through a microscope at a cell and you notice:
- everything lined up in the middle
- elongated mitotic spindle
What phase of the cell cycle is occurring?
Metaphase
What dictates where the contractile ring will form for cell division?
Metaphase plate
True or false: in a multicellular area, the cells become synchronized so that they are dividing around the same time
True
What is the primary event that must occur during anaphase and what triggers this event?
Cohesin must break down, triggered by APC/c
If you are looking through a microscope at a cell and you notice:
- cohesin has broken down
- chromosomes are at the poles of the cells
What phase of the cell cycle is occurring?
Anaphase
Anaphase requires Anaphase Promoting Complex (APC) which tags _________ with ubiquitin, leading to its degradation
Loss of this protein frees _________, an enzyme that helps break chromatids apart by digesting cohesin
Securin
Separate
If you are looking through a microscope at a cell and you notice:
- inward pinching d/t contractile ring
- chromosomes are less distinct
- beginnings of nuclear envelope
What phase of the cell cycle is occurring?
Telophase/cytokinesis
What is the effect of Cdks in the breakdown of the nuclear membrane?
Cdks phosphorylate nuclear pore proteins and laminin, causing breakdown of the nuclear membrane
What are the 2 cytoskeletal machines responsible for mechanical processes in M phase?
Mitotic spindle Contractile ring (actin)
What is characteristic of the contractile ring seen in anaphase?
Cleavage furrow
How does cytokinesis in plant cells differ from that of animal cells?
In plants, phragmoplast forms (remains of mitotic spindle - interpolar microtubules)
New cell wall forms from cellulose microfibrils, there is no pinching
What are some competitive advantages in organisms that utilize sexual reproduction?
“Reshuffling” genetic info, speeds up deletion of deleterious mutations, genetic variation favored by natural selection
What is the major driving force for genetic diversity/variation?
Mutation, closely followed by crossing over in meiosis
Compare mitosis vs. meiosis in terms of what cell type is involved with each
Germline = meiosis
Somatic cells = mitosis
Are gametes produced by the ovaries and testes at sexual maturity haploid or diploid?
Haploid
How many pairs of chromosomes in human somatic cells?
23
What does it mean to say that the two chromosomes in each of the 23 pairs in somatic cells are homologous?
They have the same genes in the same locations
Each gene has a specific location called a ______ on a certain chromosome
Locus
The 22 pairs of chromosomes that do not determine sex are called ___________
Autosomal
How many sets of chromosomes does a diploid cell have?
2 sets (2n)
What is the diploid number in humans?
46 (2n = 46)
Meiosis results in a _________ germ cell. Fertilization generates a ________ zygote.
Haploid
Diploid
For humans, the haploid number is _____
23 (n = 23)
What is the key indicator that two chromosomes are homologues?
They are the same length
What is the term describing homologues coming together for crossing over?
Synapsis
Cohesin holds sister chromatids together. What is responsible for holding tetrad homologues together?
Cohesin!
T/F Crossing over happens all along the entire length of the chromosomes
True
When does crossing over occur?
Prophase I of Meiosis I
What does haploid/diploid refer to?
The NUMBER of chromosomes. 2 sister chromatids = haploid because these still make up ONE chromosome
What is the difference in cohesin breakdown during mitosis vs. meiosis?
Mitosis - cohesin breaks down between sister chromatids at anaphase
Meiosis I - cohesin breaks down along tetrads only
Meiosis II - cohesin breaks down between sister chromatids
True/False: crossing over only occurs between sister chromatids
False! Crossing over only occurs between HOMOLOGUES
It would be pointless for sister chromatids to cross over because they are identical
When does synapsis occur during mitosis?
IT DOESN’T
3 EVENTS are unique to meiosis, and all of them occur during ___________
Meiosis I
What are the 3 events that are unique to meiosis?
- Synapsis and crossing over in prophase I
- Paired tetrads align at metaphase plate (instead of individual chromosomes)
- anaphase I involves separation of homologous chromosomes instead of sister chromatids
What carries out the actual crossing over?
Synaptonemal complexes
What is the term for areas where crossing over is currently occurring?
Chiasmata (chiasma)
What do chromosome pairing and crossing-over ensure?
Proper segregation
What are the 3 mechanisms to contribute to genetic variation outside of mutation?
Random fertilization, independent assortment of chromosomes, crossing over
How does independent assortment contribute to genetic variability?
Tetrads can line up at the metaphase plate differently; different combos lead to different possibilities
True or false: errors in meiosis may occur during crossing over and also during meiosis I or II
True
