Lecture #15: Meiosis Flashcards
Meiosis I
Prophase I
Prometaphase I
Metaphase I
Anaphase I
Telophase I
Prophase I
- Chromosomes condense and become visible
- centrosomes (MTOCs) divide and move to opposite poles
*homologous chromosomes come together (tetrad)
Synapsis = process to form tetrad
Prometaphase I
Nuclear envelope disappears
Metaphase I
Chromosomes line up in middle (metaphase plate)
- independent assortment of homologous chromosomes
- # of combinantions = 2^n
= 2^23 (humans)
> 8,000,000 combinations
Anaphase I
*homologous chromosomes seperate, move to opposite poles
- sister chromatids stay together
Telophase I
No further S - synthesis
Meiosis II
similar to mitosis
- Anaphase II = sister chromatids move to opposite poles (like mitosis)
Errors in meiosis
- Errors within a chromosome
- Whole chromosome errors
- Whole set of chromosomes error
Errors within a chromosome
Deletion: genes are deleted
Duplication: genes are duplicated
Inversion: genes are inverted
Translocation: genes end up on different chromosome
Whole chromosome error
During anaphase, one chromosome doesn’t split (nondisjuction)
Monosomy
1 copy of one of the chromosomes (ex: XO)
Trisomy
3 copies of one of the chromosomes
- leads to spontaneous abortion
Trisomy 21 = down syndrome
EX: XXX, XXY, XYY
Whole set of chromosomes error
3 sets of chromosomes - triploid
4 sets - tetraploid
- animals (including humans) will not survive, plants will (and is important to survival)
Polyploidy
important in plants
Genetic recombination
- Uniting gametes from genetically unique individuals (fertilization)
- Independent assortment of homologous chromosomes
- crossing over
- rate of natural selection depends on the genetic variation in population
