Meiosis all steps

Prophase 1

One diploid germ cell follows similar steps to mitosis…

• chromatin condenses into chromosomes and the nuclear envelope dissolves

• the centrioles move to opposing sides and form spindle fibres

• the homologous chromosomes cross over and exchange DNA

Metaphase 1

• the homologous chromosomes line up along the metaphase plate

• the spindle fibres attach to the chromasomes

Anaphase 1

• the spindle fibers pull apart the homologous chromosomes and pulls entire chromosomes to each side

Telophase 1 and cytokenesis

• the chromosomes reach the polar sides and the cell divides into two separate haploid cells

Prophase 2

similar to prophase in mitosis…

• the chromosomes condense

• new spindle fibers are formed from the centrioles that move to polar sides

Metaphase 2

• the chromosomes (sister chromatids) line up along the metaphase plate

• spindle fibers attach to the centromeres (middle of the chromasomes)

Anaphase 2

• the spindle fibers pull them apart and pull the daughter chromosomes to polar sides

Telophase 2 and cytokenesis

• chromatids reach polls and nuclear membrane reforms

• divides completely into 4 haploid unique cells

End result

1 diploid germ cell turns into 4 unique haploid gametes

how does down syndrome happen

down syndrome happens during anaphase 1 or 2

• anaphase 1 : the spindle fibres fail to pull apart the homologous chromosomes and 2 entire ones get pulled to one side resulting in one cell without a chromosome and one with extra

• anaphase 2 the spindle fibres are unable to pull apart the chromosomes into daughter chromosomes