Comparisons of recombination frequencies in hybrids involving telocentric and bibrachial wheat chromosomes

Telosomic stocks have been extensively used to map genes to chromosome arms and to determine gene-to-centromere genetic distances. It has been suggest ed that if a chromosome arm is present as a telosome, recombination frequen cies will be drastically reduced in the centromeric region. However, previo us studies have not considered the bias in recombination estimates due to s election against aneuploid gametes produced by failure of pairing at the fi rst meiotic division. Formulas are derived here for adjusting recombination estimates for this bias. Adjusted recombination frequencies between marker s located on both sides of the centomeres are analyzed in three different p airs of wheat (Triticum aestivum) isogenic segregating populations involvin g bibrachial and telocentric chromosomes. Recombination frequencies estimat ed from crosses involving telocentric chromosomes were not significantly di fferent from recombination frequencies estimated from isogenic crosses invo lving bibrachial chromosomes. The implications of the present findings for karyotype evolution, and specifically for Robertsonian fissions and fusions , are discussed.