Cytogenetics of a new type of barley with 16 chromosomes

Abstract

In the progeny of a trisomic type for chromosome 6, Purple, a 16-chromosome type was obtained, which had a pair of new metacentric chromosome 6 in excess. The new metacentric chromosome 6 was shorter than any of the 14 chromosomes of normal barley complement and showed a heteropycnotic nature at late prophase in somatic mitosis. At metaphase I in the plants with 14+one metacentric chromosome 6 (2n=15) the chromosome configuration was exclusively 7II+1I indicating that the extra metacentric chromosome 6 could not associate with the normal chromosome 6. At diakinesis and metaphase I in the new 16-chromosome plants most of the sporocytes showed 8IIor 7II+2I. Neither tetravalents nor trivalents were observed at meiosis. The chromosome behaviour at anaphase I and later stages of meiosis was regular in general, resulted in a fairly high pollen fertility of about 61 per cent. Seed fertility however, was very low. The transmission rate of the new metacentric chromosome 6 through the pollen was extremely low in 16-chromosome plants. Possible origin of new basic number and B-chromosome in diploid level through trisomic condition was suggested (Summary see p. 138).