Chromosome abnormalities and gamete production in man.

The averaged incidence of chromosome abnormalities from samples of infertile males has been estimated to be approximately 5%, of which 4% are sex chromosome abnormalities and 1% autosomal abnormalities. Variations in the frequencies among different samples are probably due to ascertainment bias. The autosomal abnormalities consist mainly of balanced translocations which are found with a frequency of nine per thousand. Most translocations are Robertsonian ones and most of them are familial. The reasons why a balanced translocation interferes with the normal meiotic process are discussed. The effects on female fertility of numerical and structural aberrations of the X chromosome are discussed with special attention to the deficiencies of the short and long arm of the X chromosome. Several of these deficiencies are secondary to X/autosome translocations transmitted by the mother of the probands. It is concluded that the function of the abnormal X chromosome rather than the loss of specific segments is probably correlated with the lack of gamete production.