THE INHERITANCE OF CHROMOSOME DEFICIENCY IN AVENA SATIVA MONOSOMICS

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Abstract
A technique is described for the calculation of the frequencies of functioning deficient and euploid male and female gametes produced by monosomics of Avena sativa (2n = 6x = 42), using the frequencies of nullisomic, monosomic and euploid plants in selfed progenies. The technique depends on the observed insignificance of nullisomic zygote inviability. Frequencies of functioning 20- and 21-chromosome gametes were estimated for 3 different monosomics in A. sativa var. Sun II, by producing reciprocal hybrids between monosomics and euploid, and by checking the frequencies of 41-and 42-chromosome plants in the F1 hybrid progenies. Results from this method are not subject to bias due to nullisomic zygote inviability. These results were found to compare closely with those obtained by the alternative technique, indicating that nullisomic zygote inviability is not important in the monosomics studied. Frequencies with which 20- and 21-chromosome male and female gametes functioned were estimated from the frequencies of 40-, 41- and 42-chromosome plants in the progenies of 13 Sun II monosomics considered to be deficient for different chromosomes. Considerable and consistent dissimilarities in the frequencies with which different monosomics segregated nullisomics were found to be due to differences in the frequencies that 20-chromosome pollen functioned. Frequencies with which 20-chromosome pollen was produced in different monosomics were found to be comparable, consequently the different frequencies at which 20-chromosome pollen functions must be due to dissimilarities either in the viabilities of pollen deficient for distinct chromosomes or in the abilities with which pollen grains deficient for different chromosomes compete with euploid pollen.