Meiosis Flashcards
Whats the DNA difference in haploid vs diploid cells
Haploid cell (n); half the amount of DNA as a diploid cell
Diploid cell (2n); 2x more DNA that a haploid cell
What does it mean that meoisis is a terminal event
Happens outside of mitosis
How many interphases are in meiosis
1
What happens in the 1st division of meiosis
The first division randomly separates homologous chromosomes. This does not happen in mitosis
What happens in the 2nd division of meiosis
The second division results in the splitting of sister chromatids, similar to mitosis
What is the result of meiosis
The end result is 4 genetically unique daughter cells, unlike mitosis
- Each genetically unique daughter cell is haploid, unlike mitosis
Where does meiosis occur
Occurs in germ (sex) cells
What does it mean that meiosis is a terminal event
Is an ending event, does not repeat
How many chromosomes do daughter cells have after meiosis
Each daughter contains half the # of chromosomes as the parents
Explain the 5 steps of prophase 1
- Chromosomes first become visible as thin threads. DNA replication is already complete
- Homologous chromosomes continue to condense and undergo synapsis (gene for gene paining)
- When synapsis is complete, each pair of homologous chromosome forms a bivalent, each chromosome consists of 2 sister chromatids
- The chromosomes continue to shorten and thicken and the chiasmata between non-sister chromatids becomes apparent
- The nuclear envelope begins to break down
Define sister chromatids
Sister chromatids: Chromatids identical to one another
Define homologous chromsomes
Homologous chromosomes: chromosomes which contain the same genes in the same order along their chromosomal arms
Define non-sister chromatids
Non- sister chromatids: chromatids not equal to one another
Define bivalent chromosomes
Bivalent: 2 chromosomes with 2 sister chromatids
Define chiasma
Chiasma: The point of contact between two (non-sister) chromatids, belonging to homologous chromosomes
Define Recombinant chromatids
Recombinant chromatids: chromatids that include contribution of the maternal and paternal chromosomes
Explain the process of crossing over
When two chromosomes — one from the mother and one from the father — line up, parts of the chromosome can be switched.
What happens in prometaphase I
Prometaphase I: spindle fibers attach to kinetochores on chromosomes
– Kinetochores orient side to side (mono-orientation)
What happens in metaphase I
Metaphase I: Homologous pairings lineup the center of the cell, with bivalents oriented randomly with respect to each other
Define: kinetochores
Kinetochores: a large proteinaceous structure that mediates interactions between chromosomal DNA and spindle-microtubule polymers
Explain anaphase I
Anaphase I: Homologous chromosomes separate, but sister chromatids do not separate
Explain telophase and I cytokinesis
Telophase I and cytokinesis: daughter cells are ready to move into prophase II
What is the ploidy levels after meiosis I
Each daughter cell now has only one set of chromosomes, so the ploidy level would be “n” after cytokinesis of Meiosis
What happens to the DNA at the end of meoisis I
Amount of DNA reduced by half
Type of DNA reduced by half
Explain prophase II
Nuclear envelope breaks down and the chromosomes condense
Explain pro-metaphase II
Spindles attach to kinetochores on chromosomes
Explain metaphse II
Chromosomes align in center of cell
Explain anaphase II
Sister chromatids separate
Explain telophase II and cytokinesis
Nuclear envelope reforms and cytoplasm divides
What is the end result of meosis in sperm vs egg cells
Sperm: creates 4 sperm cells
Egg: creates one ovum and 3 polar bodies
