Five hundred bulbs of Tulipa australis Link, and where possible the associated young flowers, have been analysed cytogenetically in four natural populations collected from the Sierra Nevada of Spain. A majority of these were diploid (2n = 24), but a few triploids (3n = 36) were present in the population from the highest altitude. All the diploid plants from three of these populations were basic homozygotes with homomorphic bivalents. In one population, however, three types of plants were identified: homozygous standard plants (80%), plants heterozygous for a large supernumerary chromosome segment (19%), and plants homozygous for its same segment (1%). The segment was located terminally on the short arm of a submetacentric chromosome. It was heteropycnotic at meiotic prophase, showed dark C-banding at metaphase I, and was visible as a prominent heterochromatic chromocentre at interphase. The segment divided reductionally in a majority of anaphase I cells (88%), which means that chiasmata tend to be excluded from the arm carrying the segment. Seeds obtained from plants homozygous for the extra segment always carried one such a segment. One-half of the seedlings of heterozygous plants are themselves heterozygotes for the extra segment, while the other half lack the segment. Finally, 11% of the seeds from bulbs without a segment turned out to be segment heterozygotes. From these results, it is deduced that the extra segment is sexually transmitted in a Mendelian fashion and that it has little or no effect on male fertility and fecundity.Key words: polymorphism, chromosomal supernumerary segment, Tulipa australis.
Chiasma redistribution in presence of supernumerary chromosome segments in grasshoppers: dependence on the size of the extra segment
