Contrasting power of the factors for fission and sexuality in a polyploid planarian
One of the biotypes of the planarian Dugesia benazzii is triploid in the somatic line, hexaploid in the female line owing to a chromosome set doubling, and diploid in the male line due to a haploid set elimination. In a population of this biotype only 50% of the oocytes are hexaploid, the others being triploid as a results of the lack of set doubling; the male line is always diploid. After a long period of laboratory culture most of the individuals became asexual and fissiparous. Almost all the oocytes of the few specimens which have remained sexual showed triploid complement; B-chromosomes also appeared. These events represent the manifestation of a new genetic background which act upon the two germ lines in different ways and moments. These topics are discussed.
KeywordsTurbellaria Dugesia reproduction karyology
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