Let's evaluate each of the statements:

(A) In transcription, adenosine pairs with uracil

This statement is correct. During transcription, adenosine (A) in the DNA pairs with uracil (U) in the RNA.

(B) Regulation of lac operon by repressor is referred to as positive regulation

This statement is incorrect. The regulation of the lac operon by the repressor is an example of negative regulation, where the repressor protein inhibits the expression of the lac genes when lactose is absent.

(C) The human genome has approximately 50,000 genes

This statement is incorrect. The human genome is estimated to have about 20,000-25,000 genes.

(D) Haemophilia is a sex-linked recessive disease

This statement is correct. Haemophilia is indeed a sex-linked recessive disorder, typically associated with mutations on the X chromosome.

Therefore, the correct statements are (A) and (D).

Hence, the number of correct statements is: two.

Option B: Two