Mendel's Assertion A on F1 Progeny

This section analyzes the Assertion (A) and Reason (R) provided about Gregor Mendel's genetic experiments.

Assertion A: F1 Progeny Observation

• Statement: In an experiment, Mendel observed that the F1 progeny plants are all tall and none are dwarf.
• Validity: This is a correct observation from Mendel's classic monohybrid cross experiments, specifically when crossing plants with contrasting traits like pure tall and pure dwarf.

Reason R: Genetic Basis of Height

• Statement: Stem height is a contrasting trait, with tall being dominant and dwarf being recessive.
• Validity: This statement is also correct. In pea plants, the allele for tall stem (denoted as $T$) expresses dominance over the allele for dwarf stem ($t$).
• Crossing a pure tall parent (genotype $TT$) with a pure dwarf parent (genotype $tt$) yields F1 offspring with the genotype $Tt$.
• The phenotype of the F1 generation is determined by the dominant allele, resulting in all plants being tall.

Explanation: Linking Assertion and Reason

Reason R directly explains why Assertion A holds true. The dominance of the tall allele ($T$) means that even though the F1 plants carry the recessive dwarf allele ($t$), they exhibit the dominant tall trait. Therefore, the observation (Assertion A) is a direct consequence of the genetic principle described (Reason R).

Final Conclusion

Both Assertion A and Reason R are accurate descriptions of Mendel's findings and the underlying genetic principles. Reason R provides the correct genetic explanation for the observation presented in Assertion A.