Question

What did the plants of F₁ progeny look like? Give their gene combination.

Answer 1

Step 1: Understand the parental cross:
- A pure tall plant (TT) is crossed with a pure short plant (tt).
- This is a cross between two homozygous parents with contrasting traits.

Step 2: Determine the F₁ gene combination:
- Each parent contributes one gene to the offspring.
- The tall parent (TT) contributes a T allele.
- The short parent (tt) contributes a t allele.
- So, all F₁ offspring have the gene combination Tt.

Step 3: Determine the appearance (phenotype):
- The gene for tallness (T) is dominant.
- The gene for shortness (t) is recessive.
- In the Tt combination, the dominant gene masks the effect of the recessive one.
- Therefore, all F₁ plants appear tall.

Step 4: Conclusion:
- The appearance of F₁ progeny is tall.
- The gene combination is Tt (heterozygous tall).

Answer 2

Step 1: Understand the F₁ progeny:
- The F₁ progeny is obtained by crossing a pure tall plant (TT) with a pure short plant (tt).
- All F₁ plants have the genotype Tt — one dominant gene (T) and one recessive gene (t).

Step 2: Dominance of the tallness gene:
- The gene for tallness (T) is dominant.
- The gene for shortness (t) is recessive.

Step 3: Expression of traits in F₁ plants:
- In the presence of a dominant gene (T), the recessive gene (t) does not express itself.
- As a result, all F₁ plants appear tall even though they carry the gene for shortness.

Step 4: Conclusion:
The gene for shortness (t) is recessive. It is masked by the dominant tallness gene (T) in the heterozygous condition (Tt), which is why it is not expressed in the F₁ generation.

Answer 3

Step 1: Understand the experiment setup:
- Mendel performed a cross between a pure tall plant (TT) and a pure short plant (tt).
- The F₁ generation obtained from this cross consisted entirely of tall plants with genotype Tt (heterozygous).

Step 2: Self-pollination of F₁ plants:
- The F₁ tall plants (Tt) were self-pollinated.
- The possible combinations of gametes are T and t from each parent.

Step 3: Use of Punnett square:
Cross between Tt × Tt results in the following combinations:
- TT (Tall)
- Tt (Tall)
- Tt (Tall)
- tt (Short)

Step 4: Ratios observed in F₂ progeny:
- Phenotypic ratio: 3 Tall : 1 Short
- Genotypic ratio: 1 TT : 2 Tt : 1 tt

Step 5: Conclusion:
- This experiment shows that traits are controlled by discrete units called genes, which are inherited in pairs.
- One gene can be dominant (T – tall) and the other recessive (t – short).
- The recessive trait reappears in the F₂ generation when an individual inherits both recessive alleles (tt).
- Hence, Mendel concluded that inheritance follows predictable patterns.