Diploid-dependent regulation of gene expression: a genetic cause of abnormal development in fish haploid embryos.

A diploid-dependent regulatory mechanism of gene expression for spatial patterning of the eye in vertebrates has been determined by analyzing the phenotypes of haploid goldfish embryos. There are two gene loci in charge of eye spatial patterning during embryonic morphogenesis. The expressional probability for each copy of the two genes in a set of chromosomes is 50%. A pair of genes in two sets of homologous or heterologous chromosomes is 100% and essential for normal gene expression. The haploid condition itself would result in the obstruction of gene expression and abnormal development because the diploid-dependent regulatory apparatus will regulate gene expression in a haploid embryo according to the same rule as in the diploid embryo.