Meiosis Revision Cards

• Chromatin condenses -> chromosomes shorten and thicken by supercoiling
• Chromosomes come together in homologous pairs to form a bivalent
• Each pair contains; the same genes @ same loci and 1 maternal & 1 paternal chromosome

• Non-sister chromatids wrap around each other & attach @ chiasmata
• Here crossing over takes place - sections of the chromatids are swapped

• The nucleolus disappears & nuclear envelope disentegrates
• A spindle forms

• Centromeres attach to the spindle fibres, chiasmata still present

• The bivalents arrange themselves across the equator of the spindle, the chromatids arranged by random assortment

• Each pair of homologous chromosomes faces the opposite pole

• One of each pair of homologous chromosomes is pulled by spindle fibres to opposite poles
• Chromatids independently segregate

• Centromeres do not divide 

• Chiasmata separate - lengths of chromatid stay on newly attached chromatid

In animal cells:

• Nuclear envelopes reform around the chromosomes at each pole
• The cell divides by cytokinesis

In plant cells:

• Cell goes straight from Anaphase I -> Meiosis II

• Nuclear envelope breaks down again

• Chromosomes supercoil

• Spindle fibres form

• Chromosomes arrange themselves on the equator of each cell and are attached by centromeres to the spindle

• Chromatids are arranged by random assortment

• Centromeres divide

• Chromatids are pulled to opposite poles by spindle fibres

• Chromatids randomly segregate

In animal cells:

• Nuclear envelopes reform around the haploid daughter nuclei
• The two cells now divide to give four haploid cells

In plants cells:

• A tetrad of four haploid cells is formed

• Meiosis is now complete

• The cell rests until the next meiotic division