Cytogenetics of hybrid introgression in Icelandic birch

Cytogenetic analysis has made it possible to describe the mechanism of introgression between two Icelandic birch species, dwarf arctic birch (Betula nana L.) and pubescent birch (Betula pubescem Ehrh.). It is suggested that the gene flow is predominantly from B. nana (2n=28) to B. pubescens (2n=56) via hybridization and subsequent backcrossing of the hybrids with B. pubescens. accompanied by selection of the introgressant type. The mechanism of such transfer is from diploid to tetraploid levels via intermediate triploids, not through the formation of aneuploid complexes.