THE ORIGIN AND BEHAVIOUR OF CHIASMATA

VI. HYACINTHUS AMETHYSTINUS

¹ JOHN INNES HORTICULTURAL INSTITUTION, MERTON, LONDON

The longer chromosomes of Hyacinthus amethystinus are on the average ten times the bulk of the shorter ones but have only twice as many chiasmata per bivalent. Thus, although the longer chromosomes form only two or three chiasmata, the shortest chromosomes regularly form one chiasma which ensures their regular pairing. This abnormality is characteristic of particular species and, like other variations in chiasma frequency and distribution, it must be genetically controlled. It is therefore to be regarded as an adaptive property.