Predict the genotypic and phenotypic ratios of the possible offspring of a male hemophiliac and a female carrier using suitable symbols for the alleles in a Punnett grid.

Genotypic ratio:

Phenotypic    ratio:
   

Hemophilia is a disorder where the ability to control blood clotting or coagulation is impaired. Describe the process of blood clotting.

correctly constructed Punnett square with correct gamete genotypes;

genotypic ratio: 1 X^HX^h : 1X^hX^h : 1 X^HY : 1 X^hY; (can be inferred from cells of Punnett square)

phenotypic ratio: 1 female hemophiliac : 1 female carrier/non-hemophiliac :
1 male hemophiliac : 1 male normal/non-hemophiliac / 50 % hemophiliac :
50 % non-hemophiliac;

Allow ECF. Award [2 max] if notation used does not indicate sex linkage, i.e. if cross is Hh×hh.

release of clotting factors from platelets/damaged cells;
conversion of prothrombin to thrombin;
thrombin catalyses the conversion of fibrinogen into fibrin;
(insoluble) fibrin (net) captures blood cells;

The words "hemophiliac‟ and "female carrier‟ should have been enough to remind the students of sex linkage. Many did not know that hemophilia was sex-linked The candidates were allowed an "error carried forward‟ mark if they had completed the Punnett square correctly but with the incorrect parents.  

The blood clotting process was not at all well known. Many interchanged fibrin and fibrinogen in terms of function and properties.