Explain why male cats with a tortoise shell do not usually occur​

In cats, males are XY and females are XX. A gene on the X chromosome controls fur colour in cats. The allele G codes for ginger fur and the allele B codes for black fur. These alleles are codominant. Heterozygous females have ginger and black patches of fur and their phenotype is described as tortoiseshell. Male cats with the tortoiseshell phenotype do not usually occur. Explain why [1]

Region b indicates the occipital lobe