Before revision: If there is no genetic information on the Y chromosome for a certain trait , the effect of the Y is neutral and the allele on his X chromosome, which would be recessive in a heterozygous woman, can now alone come to expression.
After revision: If there is no genetic information on the Y chromosome for a certain trait then the allele on his X chromosome, which would be recessive in a heterozygous woman, can now alone come to expression.