Segmental Interchange in <i>Pisum</i> II

Abstract

Some of the progeny of the previously described hybrid with an association of 6 chromosomes were studied cytologically.Two plants were found to be trisomic and structurally hybrid, one showed normal bivalent pairing and was fertile, one had an association of six and was three quarter sterile, like the parent plant, and two had a new association of 4 chromosomes. The relationship between the new association of 4 and the original association of 6 is discussed.The frequent observation of “figure-of-eight” configurations in the association-of-six forming hybrid led to the prediction that plants with associations of four would occur amongst its offspring. Since the present observations fulfil these predictions, they afford genetical evidence that segmental interchange between otherwise non-homologous chromosomes has occurred as the result of crossing-over associated with chiasma formation in an interstitial homologous segment.