Females rarely experience the physiologic defect of haemophilia because they do so only when they are:

Pick out the correct statements.
$(1)$ Haemophilia is a sex-linked recessive disease.
$(2)$ Down's syndrome is due to aneuploidy.
$(3)$ Phenylketonuria is an autosomal recessive gene disorder.
$(4)$ Sickle cell anaemia is an $X$-linked recessive gene disorder.

In the following human pedigree,the filled symbols represent the affected individuals. Identify the type of given pedigree.

In pedigree analysis,the square,blackened,and horizontal lines represent:

Phenylketonuria is a genetic disorder due to a defect in the metabolism of which of the following?

Albinism is caused by an autosomal recessive disorder. $A$ couple has their first child who is an albino (having abnormal skin pigmentation). What is the probability that their second child will also be an albino (in $\%$)?