Lecture 4b- Mitosis and Meiosis Flashcards
Meiosis
The process sexually-reproducing organisms use to create gametes with half the required genetic material to create a zygote
Bivalent and Tetrad
A bivalent is one pair of chromosomes (homologous chromosomes) in a tetrad. A tetrad is the association of a pair of homologous chromosomes (4 sister chromatids) physically held together by at least one DNA crossover
Crossing-over
Genetic recombination that occurs during meiosis, leading to novel forms
Chiasmata
A point at which paired chromosomes remain in contact during the first metaphase, and at which crossing over and exchange of genetic material occur between the strands
Recombination
The mixing of genetic material from different strands of DNA
Synapsis
An event that occurs during meiosis in which homologous chromosomes pair with their counterparts and remain bound due to the exchange of genetic information
Synaptonemal Complex
A protein and RNA structure that aids in forming the connections during synapsis of homologous chromosomes
The stages of Meiosis
- In the first cell division (meiosis I), homologous chromosomes separate
- Meiosis I results in 2 haploid daughter cells with replicated chromosomes
- In the second cell division (meiosis II), sister chromatids separate
- Meiosis II results in 4 haploid daughter cells with unreplicated chromosomes
The stages of Meiosis: Interphase
chromosomes are replicated to form sister chromatids
- the sister chromatids are genetically identical and joined at the centromere
Division in meiosis I occurs in four phases:
- Prophase I
- Metaphase I
- Anaphase I
- Telophase I
Prophase I
- chromosomes begin to condense
- each pair of chromosomes forms a tetrad, a group of 4 chromatids
Metaphase I
-tetrads line up at the metaphase plate, with one chromosome facing each pole.
Anaphase I
pairs of homologous chromosomes separate
- sister chromatids remain attached at the centromere
Telophase I and Cytokinesis
Telophase I: each half of the cell has a haploid set of chromosomes (consists of 2 sister chromatids)
prophase II
a spindle apparatus forms
- in late prophase II, chromosomes move toward the metaphase plate