9. Two mutant plants, both bearing white flowers, were crossed. All F₁ plants had red coloured flowers. When an F₁ plant was selfed it produced progeny with either red or white coloured flowers in 9:7 ratio. Based on this information, which one of the following conclusions is correct?
(1) The mutations in the parents do not complement each other
(2) The mutations in the parents are allelic
(3) The mutations in the parents are non-allelic
(4) The mutations in the parents are linked

The correct answer is (3) The mutations in the parents are non-allelic.

Step-by-step explanation

• Both parents: white flowers (mutant).

• F1 from cross: all red flowers (wild type phenotype).

  • This means each parent supplies a functional copy of a different gene needed for red pigment; together, they restore function in F1.

  • Such restoration is called complementation, indicating the mutations are in different genes (non‑allelic).

• F1 selfed → F2 ratio: 9 red : 7 white.

  • A 9:7 ratio is classic for complementary gene interaction (a form of epistasis) involving two genes, say A and B.

  • Genotypes with A_B_ → red (9 parts).

  • Any genotype lacking A or B (A_bb, aaB_, aabb) → white (7 parts).

  • This fits exactly with two different genes controlling the same trait.

Therefore, the parental mutations are in two different genes (non‑allelic) that both must have a dominant functional allele for red colour.

Option-wise analysis

1. The mutations do not complement each other

• False. F1 plants are red (wild type), so the mutant alleles complement each other; if they did not, F1 would still be white.

2. The mutations are allelic

• Allelic = in the same gene. Two recessive alleles of the same gene (a₁a₁ × a₂a₂) would give F1 a₁a₂ with no wild-type copy and thus still white. F1 is red, so mutations are not allelic.

3. The mutations are non-allelic – correct

• Different genes; each mutant provides what the other lacks, producing red F1 and a 9:7 complementary ratio in F2.

4. The mutations are linked

• Linkage refers to physical proximity on a chromosome, not to whether they produce a 9:7 ratio. The key information here is complementation and the modified dihybrid ratio, which speaks to gene interaction, not linkage.

Thus, the correct conclusion is that the mutations in the parents are non‑allelic.