Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

Robertsonian translocation is a chromosome mutation involving fusion of two acrocentric chromosomes, i.e. highly asymmetric chromosomes, that have a centromere in the vicinity of one of the telomeres. Through this fusion, one new metacentric chromosome is formed from two chromosomes, i.e. a chromosome with a centromere in the vicinity of its centre. This mutation occurs quite frequently in some organisms. If aneuploidy is not considered, this is the most common chromosomal mutation in humans, with a frequency of occurrence of approximately one for each 1000 meioses (de Villena & Sapienza 2001). In a heterozygote whose nucleus contains one haploid set with a new metacentric chromosome and one set with two original acrocentric chromosomes, meiotic division leads to the formation of chromosomal trivalents. As a consequence, part of the mature sex cells can be aneuploidal, i.e. generally nonfunctional. It often happens that functional gametes contain, with varying probability, a metacentric chromosome or, on the other hand, two original acrocentric chromosomes (Gropp, Winking, & Redi 1982; Everett, Searle, & Wallace 1996; de Villena & Sapienza 2001).As a consequence, a certain chromosome mutation can spread in an avalanche manner regardless of the fact that its presence reduces the biological fitness of its carrier. In organisms in which crossing-over occurs in high enough frequency, the proliferation of this chromosome mutation need not be accompanied by differential transfer of the alleles of the individual genes. Only the new topological structure of the chromosome spreads in the population, while the genetic content of this chromosome remains dependent on the composition of the gene pool of the relevant local population.