$A$ hereditary disease,which is never passed on from father to son,is:

Presence of a single allele of a character in a diploid organism is known as $:$

Choose the correct option for the given descriptions:
$(i)$ The heterozygous female transmits the disease to the son.
$(ii)$ Change in the shape of the $RBC$ from biconcave disc to elongated sickle-like structure.
$(iii)$ Mentally retarded.
$(iv)$ Haemoglobin is not formed in the proper amount in the blood.

Choose the correct option regarding genetic disorders and inheritance patterns.

Match the following columns.

Column-$I$	Column-$II$
$(w)$ Blood group	$(a)$ Polygenic inheritance
$(x)$ Skin colour	$(b)$ Aneuploidy
$(y)$ Mendelian disorder	$(c)$ Incomplete dominance
$(z)$ Chromosomal disorder	$(d)$ Sickle-cell anaemia
	$(e)$ Co-dominance

In a cross between genotypes showing recessive epistasis,the $F_2$ phenotypic ratio will be .....