Question

Unlike Mendel's experiments, Bateson and Punnett's experiment with sweet peas demonstrated that, in the $F_2$ generation, genes for flower color and pollen length:

• A. Assort independently
• B. Assort randomly
• C. Do not assort independently
• D. Showed chromosomal non-disjunction

Hint:

Genetic linkage is the primary exception to Mendel's Law of Independent Assortment.
The closer two genes are on a chromosome, the less likely they are to be separated by crossing over during meiosis.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Mendel's Law of Independent Assortment states that alleles for different traits segregate independently of one another during gamete formation.
This law holds true when genes are located on different chromosomes or are far apart on the same chromosome.

Step 3: Detailed Explanation:
In 1905, William Bateson and Reginald Punnett crossed sweet peas (Lathyrus odoratus) to study two traits:
1. Flower color: Purple (P) dominant over red (p).
2. Pollen shape: Long (L) dominant over round (l).
Crossing homozygous purple-long (PPLL) with red-round (ppll) produced a purple-long (PpLl) \(F_1\) generation.
Under independent assortment, selfing the \(F_1\) generation should yield a classic dihybrid ratio of \(9:3:3:1\) in the \(F_2\) generation.
However, Bateson and Punnett observed a significant deviations from this ratio.
The parental phenotypic combinations (purple-long and red-round) occurred in much higher frequencies than expected, while recombinant types were rare.
They initially described this phenomenon as "coupling and repulsion."
Thomas Hunt Morgan later explained that this deviation was caused by genetic linkage.
Because the genes for flower color and pollen shape are located close together on the same chromosome, they tend to be inherited together and do not assort independently.

Step 4: Final Answer:
Bateson and Punnett's experiment showed that the genes for flower color and pollen length do not assort independently, matching Option (C).