Q.Why are sex linked recessive characters more common in the male human beings ?

Because males carry only one X chromosome, a single recessive X-linked allele is unmasked and always expressed, while females, having two X chromosomes, are usually protected as carriers unless they inherit the recessive allele from both parents.

Sex-linked inheritance in humans mainly concerns genes located on the X chromosome, since the Y chromosome is much smaller and carries very few genes with corresponding loci to the X. A human male has the sex-chromosome constitution XY, meaning he possesses only a single X chromosome (inherited from his mother) -- he is said to be hemizygous for X-linked genes, since there is no second allele on the Y chromosome to mask a recessive allele's effect. Consequently, if a male inherits even one copy of a recessive X-linked allele (e.g., for colour blindness or haemophilia), that trait/disorder is expressed in him, since there is no dominant allele present to override it. A female, by contrast, has two X chromosomes (XX); to show an X-linked recessive trait, she must inherit the recessive allele on both her X chromosomes (be homozygous recessive) -- if she has only one copy, the normal dominant allele on her other X chromosome masks the recessive one, and she remains phenotypically unaffected, though she is a carrier who can pass the allel …