Meiosis Flashcards
What is the outcome of mitosis ? Meiosis ?
Mitosis: 2 diploid cells
Meiosis: 4 haploid cells (gametes)
How many rounds of replication and division take place in mitosis ? In meiosis ?
Mitosis: 1 round of replication 1 round of division
Meiosis: 1 round of replication 2 rounds of division
What are the main differences between meiosis and mitosis ?
- 2 diploid daughter cells vs 4 halpoid daughter cells
- 1 round of replication 1 round of division vs 1 round of replication 2 rounds of division
- Duplicated chromosomes pair early on in meiosis, unlike in mitosis
- Recombination in meiosis, not mitosis
Describe the main steps of meiosis.
P-I: Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents (by process of synapsis, come towards each other), crossing over occurs
M-I: Spindle fibres from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell
A-I: Spindle fibres contract and split the bivalent, homologous chromosomes move to opposite poles of the cell
T-I: Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells
P-II: Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)
M-II: Spindle fibres from opposing centrosomes attach to chromosomes (at centromere) and align them along the cell equator
A-II: Spindle fibres contract and separate the sister chromatids, chromatids (now called chromosomes) move to opposite poles
T-II: Chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) to form four haploid daughter cells
How do homologous chromosomes line up in mitosis ? in meiosis ?
Mitosis: Homologous chromosomes lined up at the metaphase plate independently
Meiosis 1: Homologous chromosomes are paired at the metaphase plate
What is a bivalent ?
A pair of synapsed (aligned) homologous chromosomes
What is a chiasma ? How many chiasma may there be per chromosome ?
“The points at which members of a chromosome pair are in contact during prophase 1 of meiosis and because of which recombination, or crossing over, occurs on separation”
2 or 3 chiasma along chromosome pair
What are the main features of recombination ?
- Process that creates new combinations of genes by shuffling the linear order of the DNA.
- If genes close, more likely to be inherited together
- Occurs through Holliday Junction
What is a Holliday Junction ?
the cross-strand structure formed when two DNA duplexes cross in a recombination event.
May the outcomes of a recombination event be predicted ?
No
How does pairing and recombination of sex chromosomes in males occur ?
- X and Y cannot pair perfectly (not the same size) but still pair up
- Pseudo-autosomal regions (on tip of X and on tip of Y) allow X and Y to pair up and undergo recombination.
- Rest of Y does not undergo recombination (or very little)
How may the Y chromosome be used to trace paternal ancestry ?
Because most of Y chromosome (except for pseudo-autosomal region) does not undergo much recombination so stable region of genome
What are the events in meiosis which help create genetic diversity ?
- Independent assortment of maternal and paternal homologs during meiosis 1: “Pairs of homologous chromosomes (tetrads) are lined up independently of each other (maternal and paternal chromosomes are also lined up on the metaphase plate at random)”
- Recombination: in prophase 1
What is the pause between meiosis 1 and 2 called ?
Interkinesis
What is MPF ?
Maturation Promoting Factor (a CDK-cyclin complex)