because females have a pair of X chromosomes so there are lot of chances for them to be heterozygous i.e. two different alleles and dominant allele will be expressed. They are prone to get affected only if they are homozygous. Where as males have only one X chromosome so they are prone to X linked disorders more than females
Human beings have two sex chromosomes – X and Y . Males have XY and females have XX. Y chromosome have some male specific genes ….but the x chromosome have copies of many genes which the Y chromosome is lacking and a major portion of Y chromosome is considered genetically INERT.
Thus females have two gene loci available on each X chromosome and males have only one gene locus on one X chromosome ( as the other one is Y chromosome) .
In females , the expression of sex linked trait is when it is Dominant …or if it is Recessive …then female needs to be Homozygous for it .
Whereas in the case of Males… the allele present on X chromosome will be directly expressed whether it is Recessive or Dominant ..because males have only one X chromosome .
Thus X linked traits are more frequently expressed in males than in the females.