Which of the following is a Mendelian disorder?

$A$ 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 are affected. Which of the following modes of inheritance do you suggest for this disease?

The gene for colour blindness is located on

Match the columns:

Column $I$	Column $II$
$(1)$ Albinism	$(q)$ Recessive gene represented by $cc$
$(2)$ Phenylketonuria	$(s)$ Recessive gene represented by $pp$
$(3)$ Sickle cell anaemia	$(p)$ Recessive gene represented by $Hb^sHb^s$
$(4)$ Alkaptonuria	$(r)$ Recessive gene represented by $aa$

If both parents are carriers of thalassemia,which is an autosomal recessive disorder,what is the probability of having an affected child?

Hereditary diseases constitute an important factor in checking the growth of population of a small community if: