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Figure 3.— Giemsa stained karyotype (upper row) and C-banding karyotype (lower row) of the same 



skipjack tuna. 



involved a reduction in uniarmed chromosomes to 

 form biarmed chromosomes, we would have ex- 

 pected to find a difference in the chromosome 

 number between Katsuwonus and Thunnus. 



It is probable that speciation within the genus 

 Thunnus might also be related to chromosome rear- 

 rangement because the number of chromosomes is 

 the same. Pericentric inversion is a type of intra- 



chromosomal rearrangement that could result in the 

 displacement of the centromere to convert a telo- 

 centric chromosome into a metacentric one. Zenzes 

 and Voiculescu (1975) suggested that pericentric in- 

 version was involved in the chromosomal organiza- 

 tion of the brown trout, Salmo trutta. The extent 

 to which this mechanism has been related to the 

 speciation of genera Thunnus and Katsuwonus is 



474 



