Obviously a sex-linked trait. All males seem to exhibit the trait but none of the females. It can’t just be the lack of something on the X, otherwise some of the females would have exhibited this trait as well. No, perhaps a mutant on the Y which acts in a trans & “dominant” acting manner to repress or abolish something on other chromosomes?
Note: All the males exhibit the phenotype, but none of the females do. If you accept it is a sex-linked trait which manifests because the males don’t have a compensatory copy of the allele inherited from the mother, then all their mothers had to have at least one copy of the “bad” allele. That means that random mating implies that at least 1/4 of the women in the current generation would exhibit the trait (assume that all the mothers are heterozygous), as they would inherit a “bad” copy from both parents. If all the males exhibit the trait, but none of the females do, that would imply something that acts dominantly from the Y chromosome, which only males have.
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