OBSERVATIONS ON MEIOSIS IN 3 CYTOTYPES OF BETULA-ALBA L

Meiosis was studied in three birch cytotypes; B. pendula 2n= 28, B. pubescens 2n= 56 and a type with the intermediate chromosome number 2n= 42. Meiosis was similar in B. pendula and B. pubescens and a similar range and frequency of abnormalities was found. In relation to both types there was strong circumstantial evidence that x= 7 rather than x= 14, which is commonly accepted. In addition it was also shown that in B. pubescens there exists means of producing aneuploid gametes. Meiosis in 2n= 42 trees differed greatly from that in 2n= 28 and 2n= 56 trees. Many cells contained coalesced masses of chromatin and could not be analysed. Those that were studied showed a much greater frequency of abnormality than that found in the other two cytotypes. Surprisingly, around 50 % of analysable cells showed 21:21 distribution of chromosomes at metaphase II. Although the origin of these trees is unknown it is suggested that they are not triploids but hexaploids, i.e. x=n= 7. Copyright © 1979, Wiley Blackwell. All rights reserved