Pick out the correct statements.
$I.$ Haemophilia is a sex-linked recessive disease
$II.$ Down's syndrome is due to aneuploidy
$III.$ Phenylketonuria is an autosomal dominant gene disorder
$IV.$ Phenylketonuria is an autosomal recessive gene disorder
$V.$ Sickle cell anaemia is an $X$-linked recessive gene disorder

Select the group of $CORRECT$ statements.
$I$. If phenotype of offsprings shows only the dominant trait then the parent plants are heterozygous.
$II$. $A$ true breeding line shows stable trait inheritance and expression for several generations.
$III$. In mendelian experiment material,contrasting characters can be easily recognized.
$IV$. When a single gene controls two (or more) different traits,it is called polygene.
$V$. When interactions occurs between the alleles of different genes present on the same or different chromosome it is called intragenic interaction.

How many sentences are correct?
$(i)$ Every gene contains the information to express a particular trait.
$(ii)$ Gene responsible for $\beta$-thalassemia is present on the $11^{th}$ pair of autosomal chromosomes.
$(iii)$ Mendel's approach of using mathematics to explain biological phenomena was totally new and unacceptable to many of the biologists of his time.

It is said that harmful alleles are eliminated from a population over a period of time,yet sickle cell anaemia persists in the human population. Why?

How many types of zygotic combinations are possible between a cross $Aa \; BB \; Cc \; Dd \times AA \; bb \; Cc \; DD$?

In maize, albinism is caused by the effect of: