Week 1 Objective 3: list stages of meiosis and relate to gametogenesis in males and females Flashcards
Major events in meiosis
- Pairing of homologous chromosomes
- crossing-over
- meiosis requires two consecutive cell divisions BUT only one cycle of DNA replication
- increase in cell numbers (sometimes)
- Daughter cells are not genetically identical
- Daughter cells are haploid
First stage of Meiosis
Prophase 1
- Leptotene
- Zygotene
- Pachytene
- Diplotene
- Diakinesis
Prophase 1: Leptotene
- Chromosomes are threadlike
- Each chromosome consists of two chromatids
- Chromosomes begin to coil
Prophase 1: Zygotene
Homologous chromosomes pair (synapsis)
Synaptonemal complex forms
Prophase 1: Pachytene
Maximum coiling
tetrads
crossing over begins
Prophase 1: Diplotene
crossing over continues
chiasmata are well defined
Diakinesis
Cross over complete
Terminalization
Spindle apparatus is in place
nuclear membrane is disrupted
Metaphase 1
Tetrads line up along equatorial plate
centromeres do not divide
Anaphase 1
Homologous chromosomes move to opposite poles
Each homologue consists of two chromatids
Chromatids are not genetically identical because of cross-over
Daughter cells will be haploid
Telophase 1
Cytokinesis occurs (usually)
Nuclear membranes reform (maybe)
Spindle apparatus disassembles
chromosomes may uncoil to varying degrees
Prophase II
Chromosomes again condense
nuclear membranes disappear
spindle apparatus reforms in each cell
each chromosome consists of two chromatids
each daughter cell has one complete set of chromosomes (haploid)
Metaphase II
Chromosomes line up on equatorial plate
centromeres divide
Anaphase II
Chromosomes move to opposite poles
eache chromosome consists of a single chromatid
Telophase II
chromosomes uncoil
cytokinesis is complete
nuclear membranes reform
end result if four genetically unique haploid daughter cells
