meiosis Flashcards
meiosis
Production of haploid gametes
Meiosis I
(reductional division):
* homologs pair up
Crossing Over: Nonsister chromatids exchange DNA segments
tetrad (a group of four chromatids)
chiasmata, X-shaped regions of crossing over
* homologs separate
* resulting in two haploid daughter cells with replicated chromosomes
Meiosis II
(equational division):
* sister chromatids separate
* The result is four haploid daughter cells with unreplicated chromosomes
Crossing over in Prophase I increases the possible variation
* Nonsister chromatids exchange DNA segments
* Each pair of chromosomes forms a tetrad
* a group of four chromatids
* chiasmata, X-shaped regions where crossing over occurred
Meiosis differs from Mitosis in meiosis l
- Synapsis and crossing over in prophase I:
* Homologous chromosomes physically connect and exchange genetic information - homologous chromosomes (tetrads) are paired at the metaphase plate instead of individual replicated chromosomes
- Homologous chromosomes, instead of sister chromatids, separate at anaphase I
Variation
the heritable genetic kind, results from:
1. Mutations
2. Behavior of chromosomes during meiosis
* Independent assortment of chromosomes
* each member of a pair of homologous chromosomes separates independently of the members of other pairs so the results are random
3. Crossing over - produces recombinant chromosomes
* homologous portions of two nonsister chromatids trade places
4. Random fertilization
2n = the number of combinations possible when chromosomes assort independently into gametes