Question

Given below are two statements, one is labelled as Statement (1) and other one labelled as Statement (2).
Statement (1): The flower colour in the sweet pea, are either purple or white. The \(F_1\) hybrids were all purple. When these hybrids were intercrossed, a ratio of 9 purple: 7 white plants were obtained in the \(F_2\).
Statement (2): Two independently assorting genes, C and P, are involved in anthocyanin synthesis and that each gene has a recessive allele that abolishes pigment production.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statements are correct.
• B. Statement (1) is correct but Statement (2) is incorrect.
• C. Statement (1) is incorrect but Statement (2) is correct.
• D. Both Statements are incorrect.

Hint:

The standard dihybrid ratio is \(9:3:3:1\).
Whenever you see a modified dihybrid ratio like \(9:7\), think of complementary gene action where homozygous recessive alleles at either locus mask the dominant phenotype.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
This question deals with classical genetics and non-allelic gene interactions.
Specifically, it tests duplicate recessive epistasis (also known as complementary gene action).

Step 3: Detailed Explanation:
Let us analyze the genetics of flower color in sweet pea (Lathyrus odoratus):
- Statement (1): In their historic experiments, Bateson and Punnett crossed two different true-breeding white-flowered varieties of sweet pea.
Surprisingly, all the \(F_1\) offspring produced purple flowers.
When these \(F_1\) purple hybrids were self-pollinated or intercrossed, the \(F_2\) generation segregated into 9 purple-flowered plants and 7 white-flowered plants.
Thus, Statement (1) is a historically and scientifically correct observation.
- Statement (2): To explain this \(9:7\) ratio, it was determined that purple pigment (anthocyanin) synthesis requires the functioning of two distinct genes, \(C\) and \(P\).
These genes assort independently.
A dominant allele from both loci (\(C\) and \(P\)) must be present together (\(C\_P\_\)) to complete the biochemical pathway that produces the purple pigment.
If either gene is homozygous recessive (\(cc\) or \(pp\)), or both are recessive (\(ccpp\)), the pathway is blocked.
Therefore, the recessive alleles (\(c\) and \(p\)) act to abolish pigment production.
Thus, Statement (2) is correct.
Let us verify the \(F_2\) phenotypic breakdown:
- \(9/16\) are \(C\_P\_\) (Purple)
- \(3/16\) are \(C\_pp\) (White)
- \(3/16\) are \(ccP\_\) (White)
- \(1/16\) are \(ccpp\) (White)
This results in the exact \(9:7\) complementary ratio.

Step 4: Final Answer:
Both statements are correct.
Therefore, the correct choice is Option (A).