Un nouveau système polymorphe robertsonien chez une nouvelle espèce de «Leggada» (Mus goundae Petter)
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A sample of 6 ‘Leggada’ from N'Délé (Central African Republic) morphologically different from all these studied up to now, constitue a new species, which will be described by Dr F.Petter asMus goundae Petter. The caryological analysis reveals a new robertsonian polymorphical system. The diploïd numbers are 2N=16, 17, 18 or 19, whereas theN.F. is constant and equal to 30. The 3 first pairs of autosomes, constituted by SM or MC elements are identical in the 4 types, as well as pairs V (MC) and VI (AC) morphologically constant by all individuals. The robertsonian mechanisms, from which polymorphism originates, take place at pairs IV, VII and VIII. The fourth pair, while heterozygote by 2N=19, assembling one MC and two AC elements, is homozygote and MC by 2N=18, 17 and 16; pairs VII and VIII are both constituted by two AC in the cases of 19 and 18 chromosomes; to form caryotypes with 17 and 16 chromosomes these 2 pairs will fusion: by 2N=17 the mutation is heterozygote (1 MC and 2 AC) and it becomes homozygote by 2N=16 giving birth to 2 MC. The sexual chromosomes are from TR Type (X MC andY SM).
From these observations arises the problem of low chromosome numbers (16–20) which shall be discussed in a further publication.