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

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