Is the Frequency of Chromosome Abnormalities Influenced by in Vitro Techniques?

Abstract

The very specialized process of meiosis and the fact that the zygote is the stem cell of all cells in a new individual make the period of early embryonic development vulnerable to errors of chromosome segregation. If the zygote is aneuploid, i.e. not carrying the normal diploid chromosome set, it is most likely lethal to the embryo. However, major alterations of the genome are more harmful to the embryo than minor alterations. In other words, an additional copy of a chromosome (trisomy) will be less harmful than the presence of an entire extra chromosome set (triploidy), and it is expected that trisomic embryos will develop further than triploid embryos. For example, there are several reports of autosomal and sex chromosome trisomies in live born, although malformed, calves (see Popescu, 1990 for review; Herzog and Hoehn, 1991; Agerholm and Christensen, 1993; Christensen and Juul, 1999; Ducos et al., 2000) but there are no published reports of live born polyploid calves. This is at first surprising since the reports of live born, but severely malformed, triploid or even tetraploid children suggest that polyploid calves might survive to term. The lack of reports of such calves probably reflects the fact that malformed individuals are karyotyped with a higher frequency in humans compared to domestic animals and that malformed calves are of little commercial value.