What does the given symbol represent?

Give scientific reasons: The product of phenylalanine catabolism excreted in the urine in phenylketonuria.

$A$ man and a woman do not show any apparent genetic disease. They have $7$ children ($2$ daughters and $5$ sons). Three sons suffer from the given disease,but none of the daughters are affected. Which pattern of inheritance can you suggest for this disease?

In humans,color blindness is caused by:

Both sickle cell anaemia and Huntington's chorea are

Both parents are carriers for albinism. What will be the genotype/phenotype of the first three children?