One form of hemophilia is caused by a sex-linked recessive gene. assume that a man with hemophilia marries a phenotypically normal woman whose father had hemophilia. what is the probability that their first son will have hemophilia?

When a haemophilic carrier female marries a haemiphilic man then due to ther genotypes 
 
Xc=carrier of haemophilia
Xn=normal 
Y=dont carry haemophilic genes
so here we go!
        XcY         cross with      XcXn
 
 genotypes of ther offsprings
    1=XcXc      
    2=XcXn   
    3=XcY
    4=XnY     
so from whole 4 there is 50% parobability 

           

The mother inherited her father's X chromosome so her genotype is XHXh and she produces XH and Xh gametes. 

The father's genotype is XhY and he produces Xh and Y gametes. 

The possible outcomes are XHXh normal female (carrier), XhXh (affected female), XHY (normal son) XhY (affected son) 

So the probability of an affected daugher is 1.4