The Tetrad
This video presents the same text shown beside it, spoken and on screen. It adds nothing the text does not say.
State
A tetrad is a pair of homologous chromosomes, four chromatids total, held together by chiasmata after crossing over in prophase I.
Show
Each of a cell's 23 homologous pairs forms one tetrad, so a human cell in prophase I holds 23 tetrads.
Watch for
A tetrad's four chromatids are not four separate chromosomes — separation is still divisions away.