The litter size in chromosomally polymorphic blue foxes

M äkinen , A. and L ohi , O. 1987. The litter size in chromosomally polymorphic blue foxes. — Hereditas 107: 115–119. Lund, Sweden. ISSN 0018–0661. Received December 10, 1986 About 50 % of the Finnish farm bred blue foxes have a Robertsonian translocation in a heterozygous form, whereas the distributions of the homozygous form 2n = 48 and the 2 n = 50 karyotype with two acrocentric autosome pairs seem to be nearly equal. The effect on fertility exerted by the heterozygous Robertsonian translocation was studied on the material from a blue fox farm in Finland during four years. It is concluded that there is a tendency to litter size reduction in mating groups 2n = 49 compared to the 2n = 48 and 2n = 50 mating groups. In this investigation, the 2n = 48 chromosome constitution in parental blue fox groups has every year had a slight tendency to increase the litter size. In addition, the segregation of the karyotypes within the litters of the parental 2n = 49 mating groups is in favour of the 2n = 48 karyotype. Hence, an evolutional tendency towards lower chromosome number without any acrocentric autosomes seems to be indicated.