Mendel crossed pure tall pea plants (TT) with pure short pea plants (tt) and obtained $\mathrm{F}_1$ progeny. When the plants of $\mathrm{F}_1$ progeny were self-pollinated, plants of $\mathrm{F}_2$ progeny were obtained. (a) What did the plants of $\mathrm{F}_1$ progeny look like? Give their gene combination. (b) Why could the gene for shortness not be expressed in plants of $\mathrm{F}_1$ progeny? (c) Write the ratio of the plants obtained in $\mathrm{F}_2$ progeny and state the conclusion that can be drawn from this experiment.

(a) Appearance and Gene Combination of $\mathrm{F}_1$ Progeny:

• All plants of the $\mathrm{F}_1$ progeny were tall.
• Their gene combination (genotype) was $Tt$.

(b) Reason for Non-expression of Shortness in $\mathrm{F}_1$:

• The trait for tallness ($T$) is dominant, whereas the trait for shortness ($t$) is recessive.
• A single copy of the dominant allele '$T$' is sufficient to make the plant tall, which completely masks the expression of the recessive allele '$t$' in the heterozygous state ($Tt$).

(c) Ratio and Conclusion of $\mathrm{F}_2$ Progeny:

• Phenotypic Ratio: $3 \text{ Tall} : 1 \text{ Short}$ (or $75\%$ tall and $25\%$ short).
• Genotypic Ratio: $1\,TT : 2\,Tt : 1\,tt$ (ratio of $1:2:1$).
• Conclusions:

1. Sexually reproducing organisms inherit two copies of genes (factors) for each trait, one from each parent.
2. Traits do not blend; even though the shortness trait was not expressed in the $\mathrm{F}_1$ generation, it was inherited and reappeared unchanged in the $\mathrm{F}_2$ generation.
3. Traits can be dominant or recessive.