Question

The production of anthocyanin pigments in pea flowers requires the presence of at least one dominant allele in each of two independently assorting genes, C and P. The presence of anthocyanin results in purple flowers, whereas its absence gives white flowers. A cross between two double heterozygous (CcPp) plants is performed. What is the expected ratio of plants with purple flowers to plants with white flowers?

• A. 1 : 3
• B. 3 : 1
• C. 5 : 3
• D. 9 : 7

Hint:

When reconstructing ancestral states by parsimony, try each candidate state at the focal node and count the minimum changes needed to fit all tips. If the counts tie, the node is ambiguous.

Answer 1

The Correct Option is D

Step 1: Condition for purple flowers.
- For purple colour, both genes must contribute at least one dominant allele. - Hence, the genotype must be \( C\_P\_ \) (at least one dominant C and one dominant P).

Step 2: Punnett square expansion.
Cross: \( CcPp \times CcPp \). - For gene \(C\): ratio = \(1CC : 2Cc : 1cc\). - For gene \(P\): ratio = \(1PP : 2Pp : 1pp\).

Step 3: Phenotypic classes.
- Purple flowers: Any genotype with both \(C\_\) and \(P\_\). - White flowers: Any genotype missing one dominant allele (i.e., \(cc\_\_\) OR \(\_\_pp\)).

Step 4: Probability calculation.
- Probability of purple = \( \Pr(C\_\) \(\times\) \Pr(P\_\)) = \( \frac{3}{4} \times \frac{3}{4} = \frac{9}{16} \). - Probability of white = \( 1 - \frac{9}{16} = \frac{7}{16} \).

Step 5: Final ratio.
\[ \text{Purple : White} = 9 : 7 \] Final Answer:
\[ \boxed{9:7 \ \text{ (Option D)}} \]