Supervised by Vladimir Lukhtanov, a Researcher of the Zoological Institute of the Russian Academy of Sciences and a Professor at St Petersburg University, the international team included researchers from Russia, Finland, Sweden, the Czech Republic and Spain. The team discovered a previously unknown mechanism for maintaining high fertility in hybrids whose parents have dramatically different sets of chromosomes. This work was supported by the Russian National Science Foundation and published in PNAS, one of the most influential scientific journals of the world.

Interspecific hybrids of animals and plants are often called «monsters giving hope» because they may have unusual, potentially useful traits and properties. But such hybrids are often sterile and, therefore, are the dead ends of evolution.

The scientists studied chromosomes — their structure and behaviour during cell divisions — in hybrids obtained by crossing two lines of butterflies, which differ markedly in the number of chromosomes. It was believed that such hybrids should be unviable. Contrary to expectations, hybrids showed normal development and high fecundity.

«We did not expect this», said Professor Vladimir Lukhtanov. «But even more unexpected were the reasons for this high fecundity. A deeper analysis revealed a previously unknown mechanism for maintaining high fertility in the studied chromosomal hybrids. It turned out that in meiosis (that is, in the process during which germ cells arise), inversions (change of sequence) occur of the two most fundamental events — reduction and equational divisions. As a result, the first stage of reducing the number of chromosomes, which is the stage most sensitive to chromosomal changes, is replaced by a less risky stage of separation of sister chromatids. As a result, meiosis in hybrids occurs with a minimum number of disorders, or without disorders in general, and leads to the formation of normal gametes».

The study was supported by the grant of the Russian Science Foundation No. 14-14-00541.

The study sheds light on one of the mysteries of biology: how living organisms have new, altered chromosomes and new chromosome sets. And the latter is interesting to both biologists and doctors, since chromosome changes are often triggers for both biological evolution and the development of diseases.