Lecture #2 Flashcards
What happens during Prophase I?
homologous chromosomes condense and undergo synapsis, crossing over occurs, each pair of homologous chromosomes form a bivalent, chromosomes shorten and thicken and chiasmata becomes apparent, nuclear envelop begins to breakdown
What is crossing over?
formation and exchange of the chiasma, result is that new chromosomes have bits of both parental chromosomes
What happens during Pro-metaphase I?
Spindles attach to kinetochores on chromosomes
What happens during metaphase I?
Homologous pairs line up in the center of the cell with bivalents oriented randomly with respect to each other
What happens during Anaphase I?
Homologous chromosomes separate, but sister chromatids do not
What happens during telophase I?
Daughter cells are ready . to move into prophase II, daughter cells are haploids
What happens during prophase II?
The nuclear envelope breaks down and the chromosomes condense
What happens during pro-metaphase II?
Spindles attach to kinetochores on chromosomes
What happens during metaphase II?
Chromosomes align in center of cell
What happens during anaphase II?
Sister chromatids separate
What happens during telophase II and cytokinesis?
The nuclear envelope reforms and the cytoplasm divides, produces haploid cells with half the amount of DNA
Explain the process of the male germline.
- Starts with a primordial cell which goes through mitosis
- Then becomes a spermatogonium which then continues through mitosis
- Primary spermatocyte then goes through Meiosis I
- This produces a secondary spermatocyte which undergoes meiosis II
- The cells stay connected as spermatid until cytokinesis is complete and become sperm
Explain the process of the female germline.
- Primordial germ cell goes through mitosis
- Produced an oogonium which continues through meiosis
- Primary oocyte goes through Meiosis I and stops (arrests) until it is released from the ovary and ovulated
- Produces a polar body and secondary oocyte that go through meiosis II but meiosis II also arrests until the ootid is fertilized
- Results in 3 polar bodies and one ovum
How is the cell cycle regulated?
Progression through the cell cycle is controlled by proteins that appear and disappear in a cyclical fashion, and by several enzymes that become active and inactive, also in cycles
How do cyclins work?
Cyclins bind to activate cyclin-dependent kinases (CDK) to control progression through the cell cycle, promotes cell division.
What do cyclin-CDK proteins do?
Cyclin-CDK complexes phosphorylate target proteins that promote cell division
What does M cyclin-CDK do?
Helps prepare the cell for mitosis
What does S cyclin-CDK do?
Helps initiate DNA synthesis
What does G1/S cyclin CDK do?
Prepares cell for DNA replication
What is an oncogene?
cancer-causing gene
What is a proto-oncogene?
normal genes important for promoting cell division that have the potential to become cancerous if mutated
What is a tumor supressor?
genes that encode proteins whose normal activities inhibit cell division
What difference occurs in the kinetochores during mitosis vs meiosis?
in mitosis spindle fibres attach to kinetochores that oppose each other, in meiosis spindle fibres attach to kinetochores that are side by side
