Über die durch chromosomale aberrationen verursachte Sterilität

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Abstract
Summary A decrease of fertility can be caused by chromosomal aberrations of two different types: 1) Inversions and transpositions Aneuploid gametes will only be formed, if crossingover had happened between the breakpoints. A possible regulation against this sterility is avoiding any crossingover in the organism. Especially mechanisms in oogenesis and spermatogenesis are developed against paracentric inversions only. 2) Reciprocal translocations Aneuploid gametes are the result of adjacent segregation of the chromosomes involved in the translocation. The percentage of sterility is correlated with the relation of alternate and adjacent segregation. At random segregation results a relation of 2∶4 between euploid and aneuploid gametes resp. 66% sterility. But in literature there are described all possible relations between euploid and aneuploid gametes; this not only in different genera but also in populations of a species (per example in crossing experiments). These facts, especially the results of crossing experiments beget the hypothesis, that segregation of the chromosomes involved in a translocation is under strict genetic control. We postulate, that it is attributable to a single, Mendelian factor, called “sg”. This factor exists in a series of multiple alleles causing different relations between alternate and adjacent segregation. The allelomorph causing a higher fertility is dominant over the allelomorph, producing less euploid gametes. The percentage of sterility resp. fertility due to a translocation is not constant, but can be changed by mutual events. The individuum possessing the allele for more fertile gametes — without respect whether homo- or heterozygotous — will produce more offspring than another individuum with lower regulating alleles. So the alleles for sterility will be lost in the course of evolution. Finally, only individuals of a species with complete fertility (sg4/sg4) will survive in spite of segmental interchange (like Oenothera ssp., Periplaneta americana etc.). These mechanisms of regulation against sterility due to chromosomal aberrations are of interest in view of pest control with genetic methods.