Hybrid speciation in mammals: Illusion or reality?
- L. A. Lavrenchenko
- Biology Bulletin Reviews
MAMMALIAN chromosomes are, with some justification, generally considered difficult to study. Adequate techniques are thus of even more importance than with more favourable material. Faulty observations, even within recent years, have often been the direct result of poor techniques. Yet developments in the handling of mammalian chromosomes have lagged far behind the progress made by the smear and squash techniques which are used for plants. Section cutting by the microtome is still the rule for mammals with the osmium chromic mixtures, introduced by Minouchi (Darlington and La Cour, 1947) as the most commonly used fixative. After many years of work on mammalian chromosomes, Matthey (1951 a) has in fact come to the conclusion that the Minouchi technique—" and only this technique "—gives good results with mammals. Many species of mammals have a large number of small chromosomes. Apart from any labour saving in the absence of section cutting, squash techniques are thus often necessary for correct observations. The Minouchi type of fixative does not, however, lend itself well to the making of squashes. 1 have therefore examined a variety of mammals in order to study the possibility of making good squash preparations from the testes. This study has shown that a simple squash technique, far from being inferior to the Minouchi method followed by section cutting, can produce better results. I have been able to check chromosome numbers in this way and some previously recorded numbers proved to be incorrect. Correct determination has further shown a clear example of polyploid evolution in mammals which had previously been oveflooked. There are thus different reports of chromosome numbers and different reports of techniques. These involve a conflict about facts. On the other hand, the supposed absence of polyploids (Muller, 1940) and the supposed value of "fundamental numbers" (Matthey, 1951 a) involve a con ifict about theory. Application of the correct techniques has given the correct chromosome number. Application of the correct theory has given the correct explanation.