Figure 4.

The Four Core Genotypes (FCG) model.

In this Punnett square, the maternal genotype is depicted on the left-hand side and the paternal genotype is depicted at the top. A gamete from each parent carries a single sex chromosome, which come together to create the two possible offspring genotypes, XX (green column) and XY⁻ (blue column). Furthermore, the father carries Sry as a transgene, the inheritance of which determines the gonadal sex of the offspring: female above the dashed line (XX, XY⁻), and male below the dashed line (XXSry, XY⁻Sry). The FCG model can therefore be used to separate sex chromosome effects (XX, green; XY, blue) from gonadal sex hormone effects (ovarian hormones above dotted line, and testicular hormones below dotted line) in mouse.