Chapter 9.4 Flashcards
Meiosis takes place in what cell
germ cells a diploid cell ( only gametes are haploid)
before meiosis a germ cell must first undergo
Interphase in mitosis and meiosis are the same -review
- In g1 of interphase : cell grows and synthesizes the molecules necessary for division.
- S Phase : all of the cell’s DNA replicates resulting in 2 identical sister chromatids attached to a centromere. The cell also produces proteins and other enzymes necessary for the cell to divide
- G2: the chromatin begins to condense, and cell produces the spindle proteins that will move the chromosomes
The 2 parts of Meiosis
Meiosis I: Homologous chromosomes find each other then split up
Meiosis II: A second round of meiosis preceded by a 2nd interphase yield 4 haploid cells
The stages of PROPHASE I
PROPHASE I ( early) : 1. replicated chromosomes condense and become visible
PROPHASE I (late) : 1. Spindle forms as the centrosomes move to poles of the cell
- The nuclear envelope breaks allowing spindles access to the chromosomes
- The Homologous chromosomes pair up with each other. This prepares them for crossing over.
- CROSSING OVER OCCURS
- The paired homologs align at the equator of the cell
2. Spindle fibres attaches to the kinetochores assembled at each centromere.
homologous chromosomes get pulled to opposite poles of the cell.
- SISTER CHROMATIDS REMAIN ATTACHED
TELOPHASE I AND CYTOKENISIS
- nuclear envelopes form around chromosomes which may temporarily condense.
- Spindles disappear
- ( Cytokinesis may divide cell into 2 in most species)
yields four haploid cells
- spindle forms
2. Nuclear envelop breaks up
Chromosomes align along the equator of the cell
- spindle fibres attaches to the centromeres
1 The centromeres finally split
- separated sister chromatid separate to opposite poles
- nuclear envelopes form around the separated sets of chromosomes
- spindle fibres are gone
- cytokinesis separates the nuclei into individual cells
The overall result of meiosis is
one diploid germ cell has divided into four haploid cells
What must occur before Meiosis II begins
a second round of interphase but replicates only once