$Escherichia \ coli$ is an important material for genetic experiments because

Read the following four statements ($1$ to $4$):
$1$. In transcription,uracil pairs with adenosine.
$2$. Regulation of $lac$ operon by a repressor is referred to as positive regulation.
$3$. The human genome contains approximately $50,000$ genes.
$4$. Haemophilia is a sex-linked recessive disease.
How many of the above statements are correct?

The substitution of one purine $N_2$ base with another purine base or one pyrimidine $N_2$ base with another pyrimidine base is known as:

The base sequence of a segment of $DNA$ is $AAG, GAG, GAC, CAA, CCA$. Which of the following sequences represents a frame-shift mutation?

What are informosomes?

Match the following columns correctly.

Column $I$	Column $II$
$(a)$ $m-RNA$	$(i)$ Found in ribosomes
$(b)$ $t-RNA$	$(ii)$ Carries information from $DNA$ to the cytoplasm for protein synthesis
$(c)$ $r-RNA$	$(iii)$ Contains $75$ nucleotides
$(d)$ $RNA$	$(iv)$ $A$ polynucleotide chain containing ribose sugar and uracil base,existing in three types