(a) Why is the F1 progeny always of tall plants when a tall pea plant is crossed with a short pea plant?

(b) How is F2 progeny obtained by self-pollination of F1 progeny different from F1 progeny? Give reason for this observation.

(c) State a conclusion that can be drawn on the basis of this observation.

(a) Why $F_1$ progeny is always tall:

When a tall pea plant ($TT$) is crossed with a short pea plant ($tt$), the $F_1$ progeny inherits one copy of the gene (factor) from each parent, resulting in the heterozygous genotype $Tt$. In this combination, the tallness trait ($T$) is dominant because a single copy of '$T$' is sufficient to make the plant tall. The shortness trait ($t$) is recessive and is not expressed in the presence of the dominant allele. Therefore, all $F_1$ plants are tall.

(b) Difference between $F_2$ and $F_1$ progeny and the reason:

• Difference: The $F_1$ progeny consists entirely of tall plants, whereas the $F_2$ progeny (obtained by self-pollination of $F_1$) contains both tall and short plants in a phenotypic ratio of $3:1$ (where one-quarter or $25\%$ of the plants are short).
• Reason: The $F_1$ tall plants ($Tt$) carry both the dominant tallness allele ($T$) and the recessive shortness allele ($t$). When these $F_1$ plants undergo self-pollination, the alleles segregate during gamete formation. The random fusion of gametes results in three genetic combinations: $TT$ (tall), $Tt$ (tall), and $tt$ (short). The short trait is expressed in the $F_2$ generation because the recessive alleles come together in the homozygous state ($tt$).

(c) Conclusion:

Based on these observations, we can conclude that:

1. Two copies of genes (factors) control each trait in sexually reproducing organisms, with one copy inherited from each parent.
2. Traits can be dominant or recessive: A dominant trait is expressed even when only one copy is present (heterozygous state, $Tt$), whereas a recessive trait is expressed only when both copies are identical (homozygous state, $tt$).
3. No blending of traits: The traits do not mix or blend in the $F_1$ generation; they remain distinct and segregate (separate) during gamete formation, allowing the recessive trait to reappear unchanged in the $F_2$ generation.