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In this schapter of AS/A-Level Biology, we will learn about the process and significant of meiosis
Prophase I
- Chromatin condenses, supercoil, shorten and thicken. Come together in homologous pairs forming bivalents
- Non-sister chromatids wrap around each other and attach at chiasmata where crossing over may occur.
- Nucleolus disappears, nuclear envelope disintegrates.
- Spindle forms.
Metaphase I
- Bivalents line up across the equator of the spindle attached to fibres at centromeres.
Anaphase I
- Homologous chromosomes pulled by spindle fibres to opposite poles—centromeres do not divide.
- Chiasmata separate.
Telophase I
- two new nuclear envelopes form around each set of chromosomes and the cell divides by cytokinesis. Brief interphase and chromosomes uncoil.
Prophase II
- Nuclear envelope breaks down again.
- Nucleolus disappears, chromosomes condense, spindles form.
Metaphase II
- Chromosomes arranged on equator of spindle, attached by centromeres.
- Random assortment
.
Anaphase II
- Centromeres divide, chromatids pulled to opposite poles by spindle fibres.
- Chromatids randomly segregate.
Telophase II
- Nuclear envelopes reform around the haploid daughter nuclei.
- two cells now divide to give four haploid cells.
This is the end of this topic
Drafted by Harris