A Correlation Between Cytogenetic and Genetic Crossing-Over. The blue dot represents a cytologically visible knob. The hybridization of two individuals of the genotypes and karyotypes depicted in row P results after crossing-over in the F 1 types below. Nuclei with a multiple of the simple set of chromosomes are deviations. They are said to be polyploid .
Polyploidy is common in many plant species.
Within an individual can single nuclei or the nuclei of certain tissues be polyploid while the others are diploid. Such an organism is also refered to as a cytochimera . Cytochimeras can be regarded as genetic mosaics. Regarding the distribution of the different genotypes, it is distinguished between sectorial and periclinal chimeras . This is the case with many known cultured plants and also with 30-50 percent of all the wild growing angiosperms of temperate climates.