Chromosomal Causes for Fertility Reduction in Mammals

Abstract

It has long been realized that chromosome mutations, whatever their mode of induction, usually have consequences for the fertility of their carrier. In fact, this characteristic is used in mutagenicity tests, such as the heritable translocation assay, to establish the frequency of this genetic endpoint. There are two possible reasons for a reduction in fertility accompanying chromosome mutations. First, the production of gametes can be interrupted somewhere in the spermatogenesis or oogenesis process. A reduction of the number of stem cell spermatogonia or primary oocytes can be anticipated. This point has received little experimental attention, however. The second reason is that the chromosome mutation through the course of the meiotic divisions, gives rise to genetically unbalanced gametes, which usually function properly but lead to embryonic and/or fetal death. It will be apparent in what follows that in situations where genetically unbalanced gametes are produced through chromosome mutation there can be an increased frequency of germ cell death throughout the various stages of spermatogenesis. In addition, the initial number of stem cell spermatogonia or primary oocytes may be reduced. In this chapter the effect of numerical chromosome aberrations of the sex chromosomes on gametogeneris and gamete quality are discussed first.