A researcher used the CRISPR-Cas9 system and observed a different type of mutation in two alleles of a target gene in a T₀ transgenic plant. These mutations are designated as follows:

• Allele 1: Addition of a nucleotide
• Allele 2: Deletion of a nucleotide

The observed mutations can be classified as:

Correct option is B

Explanation:

• Monoallelic mutations (Option 1) – Incorrect:

  • Monoallelic means only one of the two alleles is mutated, but here both alleles have mutations.

• Biallelic heterozygous mutations (Option 2) – Correct:

  • Biallelic means both alleles of a gene are mutated.
  • Heterozygous means the mutations are different in each allele (one has a nucleotide addition, the other has a deletion).
  • Since both alleles are mutated differently, the classification is biallelic heterozygous mutations.

• Biallelic homozygous mutations (Option 3) – Incorrect:

  • Homozygous means both alleles have the same mutation, but here, one allele has an addition and the other has a deletion.

• Chimeric mutations (Option 4) – Incorrect:

  • Chimeric mutations occur when multiple different genotypes exist within a single organism, often due to somatic mutations.
  • In this case, the mutations are present only at a single gene locus in both alleles, so it's not classified as chimeric.

Thus, the correct classification is Biallelic heterozygous mutations (Option 2).

Information Booster

1. CRISPR-Cas9 is a genome-editing tool used to introduce targeted mutations.
2. Biallelic mutations mean both copies of a gene have been mutated.
3. Heterozygous mutations mean the two alleles have different mutations.
4. Homozygous mutations mean both alleles have identical mutations.
5. Chimeric mutations result from mosaicism, where different cells in the organism carry different genetic mutations.
6. Gene editing in plants using CRISPR can introduce targeted insertions, deletions, or substitutions.