MEIOTIC LAMPBRUSH CHROMOSOMES IN TURKEY, MELEAGRIS-GALLOPAVO (GALLIFORMES, MELEAGRIDAE)

Lampbrush chromosomes from turkey (Meleagris gallopavo) oocytes were studied. Five macrobivalents (four autosomes and a sex ZW bivalent) were identified and described. Comparison of the lampbrush chromosomes with previously studied chicken lampbrush chromosomes revealed that even phylogenetically close avian species demonstrate multiple changes in lampbrush chromosome morphology, although analysis of their mitotic chromosomes shows only a few inversions and Robertsonian translocations. This suggests a changed spectrum of sequences transcribed during oogenesis, even in closely related avian species. For example, most turkey lampbrush microchromosomes have giant marker loops on one of the telomeres. Some of them are more than 210 mum, i.e., 672 kb, in outline length. Such loops were not observed in chicken microchromosomes. Our results also suggest the lampbrush chromosome telomere and subtelomere marker loops to be the most variable part of the Galliformes karyotype. Variations in the marker loop pattern are thought to be related with variations in structure or transcription of chromosome heterochromatic regions. The chiasma frequency in turkey oocyte chromosomes was calculated. The average number of chiasmata in the largest turkey bivalent, A, was 8.1 +/- 0.35. In bivalents B-D, 4.0 +/- 0.26, 3.0 +/- 0.26, and 2.4 +/- 0.24 chiasmata, respectively, were found. Microchromosomes, as a rule, have one chiasma. A comparison of these results with literature data showed that the recombination rate in female Meleagris gallopavo was equal to or only nonsignificantly greater than, that of males.