A man and a woman, who do not show any apparent signs of a certain inherited disease, have seven children (2 daughters and 5 sons). Three of the sons suffer from the given disease but none of the daughters is affected. Which of the following mode of inheritance do you suggest for this disease?

 Sex-linked recessive traits typically occur only in males. Because the sex-linked trait is invariably X-linked, males transmit the trait only to their daughters, all of whom become carriers. Carrier (heterozygous) females can then transmit the trait to 50% of their male and female offspring. Affected males are hemizygous for the X-linked trait.