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| Modern Genetic Analysis Chapter 8. Chromosome Mutations The Overall Incidence of Human Chromosome Mutations Chromosomal mutations arise surprisingly frequently in human sexual reproduction, showing that the relevant cellular processes are prone to a high level of error. This is graphically depicted in Figure 8-28, which shows the estimated distribution of chromosomal mutations among all human conceptions that developed sufficiently far to implant in the uterus. Of the estimated 15 percent of spontaneous abortions (pregnancies that terminate naturally), fully half are due to chromosomal abnormalities. Some medical geneticists believe that even this high level is an underestimation, because many cases are never detected. Among live births, 0.6 percent have chromosomal abnormalities, resulting from both aneuploidy and chromosomal rearrangements.

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