Question

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

Answer 1

Step 1: Analyze Parental Cross:
- Pure tall (TT) is crossed with pure short (tt).
- This is a cross between two homozygous parents with contrasting traits.

Step 2: Determine F₁ Genotype:
- Each parent provides one allele to the offspring.
- The tall parent (TT) provides a T allele.
- The short parent (tt) provides a t allele.
- Consequently, all F₁ offspring have the genotype Tt.

Step 3: Determine F₁ Phenotype:
- The allele for tallness (T) is dominant.
- The allele for shortness (t) is recessive.
- In the Tt genotype, the dominant allele conceals the effect of the recessive one.
- Thus, all F₁ plants exhibit the tall phenotype.

Step 4: Summary:
- F₁ progeny phenotype is tall.
- F₁ progeny genotype is Tt (heterozygous tall).

Answer 2

Step 1: F₁ Progeny Generation:
- F₁ progeny results from crossing a homozygous tall plant (TT) with a homozygous short plant (tt).
- All F₁ plants exhibit the genotype Tt, possessing one dominant allele (T) and one recessive allele (t).

Step 2: Allele Dominance:
- The allele for tallness (T) is dominant.
- The allele for shortness (t) is recessive.

Step 3: Phenotype Expression in F₁ Plants:
- In the presence of the dominant allele (T), the recessive allele (t) remains unexpressed.
- Consequently, all F₁ plants display the tall phenotype, despite carrying the allele for shortness.

Step 4: Summary:
The allele for shortness (t) is recessive. It is obscured by the dominant tallness allele (T) in the heterozygous state (Tt), leading to its inhibition of expression in the F₁ generation.

Answer 3

Step 1: Understand the experiment setup:
- Mendel crossed a pure tall plant (TT) with a pure short plant (tt).
- The F₁ generation was entirely tall plants with genotype Tt (heterozygous).

Step 2: Self-pollination of F₁ plants:
- The F₁ tall plants (Tt) were self-pollinated.
- Each parent could produce gametes T or t.

Step 3: Use of Punnett square:
Cross between Tt × Tt yields 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:
- Traits are controlled by discrete units called genes, 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 two recessive alleles (tt).
- Hence, Mendel concluded that inheritance follows predictable patterns.