Which of the following statements is not correct?

The correct answer is Option (4) → UV radiations cannot cause mutations in organisms – it is not a mutagen.

A mutagen is any chemical or physical factor that causes mutations, that is, changes in the DNA sequence. The question asks for the statement that is not correct.

Option (1) Colour blindness is a sex-linked recessive disorder. — A correct statement. The defective genes lie on the X chromosome, so the disorder is sex-linked. It is recessive, and it is far more common in males than in females.

Option (2) In the pedigree analysis the inheritance of a particular trait is represented in the family tree over generations. — A correct statement. A pedigree is a family tree that traces a trait over several generations. It shows whether the trait is dominant or recessive.

Option (3) Mutation results in alteration of DNA sequences and changes in the genotype and the phenotype of an organism. — A correct statement. This is the book’s definition of mutation: a change in the DNA sequence that changes the genotype and the phenotype.

Option (4) UV radiations cannot cause mutations in organisms – it is not a mutagen. — Not correct. UV radiation can cause mutations, so it is a mutagen. The statement says the opposite.

NCERT Extract:
Mutation – “Mutation is a phenomenon which results in alteration of DNA sequences and consequently results in changes in the genotype and the phenotype of an organism. … However, there are many chemical and physical factors that induce mutations. These are referred to as mutagens. UV radiations can cause mutations in organisms – it is a mutagen.”
Mendelian Disorders – “… Colour Blidness : It is a sex-linked recessive disorder due to defect in either red or green cone of eye resulting in failure to discriminate between red and green colour.”
Pedigree Analysis – “… In the pedigree analysis the inheritance of a particular trait is represented in the family tree over generations.”