Abstract
Genetic markers were used to determine the male and female gametophytic transmission frequencies of the univalent chromosomes from doubly univalent hybrids of Triticum aestivum x Substitution Race I of T. aestivum. The 2 univalent chromosomes were 5A of wheat and I of Secale cereale. The 21 chromosome male gametophytes were the most competitive, the presence of the alien chromosome appreciably compensating for the loss of the normal chromosome. A modification of the procedure for deriving alien substitution races from alien addition races was suggested.