Meiosis

Gametes

The end products of meiosis. These are haploid (n) reproductive cells (sperm and egg) that contain only half the original genetic material.

Homologous Chromosomes

A pair of chromosomes (one from mom, one from dad) that are the same size and contain the same genes, but potentially different versions (alleles).

Tetrad

A structure formed during Meiosis I when two homologous chromosomes (four total chromatids) "hug" or pair up tightly.

Prophase I

Homologous chromosomes pair up to form tetrads. Crossing over occurs (chromosomes swap DNA—same amount).

Metaphase I

Homologous pairs line up side-by-side at the equator. This is "Independent Assortment."

Anaphase I

Homologous pairs separate and move to opposite poles. Crucial: Sister chromatids stay together.

Telophase I

Two haploid clusters of duplicated chromosomes form; cytokinesis splits the cell into two.

Prophase II

Spindle fibers reform in the two new haploid cells. No crossing over here.

Metaphase II

Chromosomes line up single-file at the equator (just like mitosis).

Anaphase II

Sister chromatids finally separate and move to opposite poles.

Telophase II

Nuclear envelopes reform around four sets of daughter chromosomes.

Cytokineses

• After Meiosis I: Results in 2 haploid daughter cells. These cells are unique because of crossing over, but their DNA is still in the "X" shape (duplicated).

• After Meiosis II: Results in 4 haploid gametes. In males, these are 4 sperm; in females, this usually results in 1 functional egg and 3 "polar bodies" that degrade.

Product/Result

4 Daughter Cells, all genetically unique, gametes.