Bird Cytogenetics

Chromosomes are the quintessence of biological dynamism. As carrier of genes,
they are the controllers of varied biological activities – the basis of life. Their
precise movement during cell-division and their amazing power of replication are
a few instances of extreme vitality.

In order to work out the chromosomal make-up of certain species of birds and to ascertain the presence of true variability, if any, in natural breeding populations, five species of birds viz. Turnix suscicator, Ceryl rudis, Merops orientalis, Sturnus contra and Treron phoenicoptera were selected for the current investigation. The harvesting of chromosomes was done, in vivo, from the bone-marrow cells.

The size distinction between the macro - and micro - chromosomes was sharp in all species, except Ceryl rudis and Merops orientalis wherein, owing to continuing drop in the size of autosomes, it became difficult to draw a line of demarcation. Finally, we relied on the criterion of De Boer (1976) to separate out the macrochromosomes from microchromosomes.

In all species, sex determination was found to be ZZ-ZW type - the female being heterogametic. Nonetheless, in T. suscicator, it was unfeasible to individualize Z & W, from a cluster of large autosomes, as both of them (sex chromosomes as well as autosomes) had similar morphology.

Four out of five species, worked out during the present investigation, had 82 number of chromosomes (n = 41) and all of them were monomorphic.  Conversely, T. phoenicoptera alone had nine diverse karyological combinations (table-9) because of two separate pericentric inversions - one in chromosome - 1 and another in chromosome - 2.

Presence of such an extensive polymorphism in T. phoenicoptera should aptly be described as an incidence of multiple chromosomal heteromorphism.