Three metaphase configurations of one set of homologous chromosomes in tetraploid meiosis.A. two bivalents; B. “cross-type” quadrivalent; C. “parallel” quadrivalent. In a cross-type quadrivalent two branches contain the tops of two chromosomes, and two branches the bottoms of two chromosomes; the location of the chromosome exchange point (the position where the branches meet) may vary between meioses.
Voorrips and Maliepaard BMC Bioinformatics 2012 13:248 doi:10.1186/1471-2105-13-248