Mitotic chromosome studies carried out on a newborn male infant with congenital abnormalities and on his family members showed that the father and paternal grandmother were heterozygotes for an unequal pericentric inversion. The child appeared to have inherited a recombinant duplication/deletion chromosome. The results of meiotic studies carried out on a testicular biopsy from the father were used to ascertain the risk of recurrence of chromosomal abnormalities in future pregnancies. A model is presented which permits the analysis of C-banded diakinetic chromosomes as to whether crossing-over has occurred within the inversion segment or not. In the present study, it was estimated that either one or two cross-overs had occurred in 52 % of the cells within the inversion segment. This would result in approximately 26% of the spermatozoa carrying either one of two types of duplication/deficiencies of chromosome No. 4.

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A Dutch population of Crenobia alpina was found to have a chromosome number of 2n = 42. One pair of large chromosomes is acrocentric and probably shows a secondary constriction; one small pair is acrocentric as well. All other chromosomes are metacentric or sub-metacentric; it has not been possible to discriminate with certainty between them. According to the hypothesis of DAH~ (1958) populations with 2n = 42 are autohexaploid, the basic genome consisting of seven chromosomes. On basis of the karyotype it was concluded that the Dutch population described here, is not autohexaploid but functionally diploid, perhaps allohexaploid.

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