Nouvelles contributions à la cytogénétique desMus Africains du sous-genreLeggada

Summary The author describes four new chromosome complements in the African pigmy-mice (Mus, subgenusLeggada). (1) One form from Angola has 18 metacentric chromosomes (N.F.=36) in both sexes. In contrast toMus minutoïdes minutoïdes Smith from South Africa, whose females have the same chromosome complement while the males show an acrocentric and shortY-chromosome, we have here a metacentricY. It is a confirmation of the hypothesis that theY ofM. m. minutoïdes was primarily of translocated type (TR) but lost a big intercalary segment of the autosomic arm. (2) In another species from Angola 2N=34;N.F.=36. It is the first case in the subgenus where a Robertsonian fusion occurs between autosomes before the transformation of the sex-chromosomesPR into sex-chromosomesTR. This observation is a confirmation that the complement 2N=36;N.F.=36 is the primitive one, being found in the three groups of species,minutoïdes, bufo-triton andtenellus. (3) Indeed, from Ghana, I have got specimens ofM. tenellus. We have here to deal with the primitive chromosome complement: 2N=36;N.F.=36. (4) In a sample of 12Leggada from the region of Bukawu (Congo), there are 5 and 7 . 4 show a total deletion of the short arm of theX-chromosome. In spite of the absence of X _dc -Y and of X _dc -X _dc in the sample, it is probable that neither of these complements is lethal.