Question

Why only tall pea plants were observed in \( F_1 \) progeny?

Answer 1

Step 1: Recall Mendel's experiment on height in pea plants.
Mendel crossed a purebred (homozygous) tall pea plant (TT) with a purebred (homozygous) short pea plant (tt). Tallness is dominant over shortness.
Step 2: Understand the terms dominant and recessive.

• Dominant trait: The trait that expresses itself in the \( F_1 \) generation and masks the expression of the other trait. Here, tallness (T) is dominant.
• Recessive trait: The trait that remains hidden or suppressed in the \( F_1 \) generation but reappears in later generations. Here, shortness (t) is recessive.

Step 3: Show the cross using Punnett square.
Parental generation: Tall plant (TT) × Short plant (tt) Gametes from tall plant: T, T Gametes from short plant: t, t \[ \begin{array}{c|cc} & T & T \\ \hline t & Tt & Tt \\ t & Tt & Tt \\ \end{array} \]
Step 4: Analyze the \( F_1 \) generation.
All \( F_1 \) progeny have the genotype Tt (heterozygous). Since T (tall) is dominant over t (short), all plants express the tall phenotype.
Step 5: Reason for only tall plants in \( F_1 \).
Only tall plants were observed in \( F_1 \) progeny because:

• The allele for tallness (T) is dominant over the allele for shortness (t).
• All \( F_1 \) plants inherit one dominant allele (T) from the tall parent and one recessive allele (t) from the short parent.
• The dominant allele masks the expression of the recessive allele, resulting in all plants being tall.

Step 6: Final answer.
Only tall plants appeared in \( F_1 \) because tallness (T) is dominant over shortness (t). All \( F_1 \) plants are heterozygous (Tt) and express the dominant trait.

Answer 2

Step 1: Recall the method used by Mendel.
After obtaining the \( F_1 \) generation (all tall plants), Mendel wanted to study the inheritance pattern further. He allowed the \( F_1 \) plants to undergo self-pollination (or self-fertilization).
Step 2: Explain self-pollination.
Pea plants are naturally self-pollinating. Mendel allowed the \( F_1 \) hybrid plants (Tt) to self-pollinate, meaning the pollen from a flower fertilizes the same flower or another flower on the same plant.
Step 3: Show the cross for \( F_2 \) generation.
\( F_1 \) generation: Tt (tall) × Tt (tall) through self-pollination Gametes from each \( F_1 \) plant: T and t \[ \begin{array}{c|cc} & T & t \\ \hline T & TT & Tt \\ t & Tt & tt \\ \end{array} \]
Step 4: Result of \( F_2 \) generation.
The \( F_2 \) progeny showed:

• Genotypic ratio: 1 TT : 2 Tt : 1 tt
• Phenotypic ratio: 3 tall : 1 short

The recessive trait (short) reappeared in \( F_2 \) generation.
Step 5: Final answer.
\[ \boxed{\text{Mendel obtained \( F_2 \) progeny by allowing the \( F_1 \) hybrid plants to undergo self-pollination.}} \]

Answer 3

Step 1: Define dominant and recessive traits.

• Dominant trait: The trait that expresses itself in the \( F_1 \) generation and masks the expression of the other trait in a heterozygous condition.
• Recessive trait: The trait that remains hidden or suppressed in the \( F_1 \) generation but reappears in later generations when present in homozygous condition.

Step 2: Identify one key difference.
The main difference between dominant and recessive traits is: A dominant trait is expressed in both homozygous (TT) and heterozygous (Tt) conditions, while a recessive trait is expressed only in homozygous condition (tt).
Step 3: Explain with example.
In Mendel's experiment on pea plant height:

• Tallness (T) is dominant \(\Rightarrow\) expressed in TT and Tt plants
• Shortness (t) is recessive \(\Rightarrow\) expressed only in tt plants

In \( F_1 \) generation (Tt), only tall trait is expressed because the dominant allele masks the recessive allele.
Step 4: Additional differences (for reference).
Other differences include:

• Dominant trait appears in \( F_1 \) generation; recessive trait does not appear in \( F_1 \).
• Dominant trait requires only one allele for expression; recessive trait requires two alleles for expression.
• Dominant trait is represented by capital letter (T); recessive trait is represented by small letter (t).

Answer 4

Step 1: Recall Mendel's experiments with pea plants.
Mendel conducted monohybrid crosses (crossing two plants differing in one trait, e.g., tall × short) and made careful observations about the \( F_1 \) (first filial) generation.
Step 2: Observation 1 - Uniformity in \( F_1 \) progeny.
All \( F_1 \) progeny plants showed the same trait (were uniform). In the cross between tall and short pea plants, all \( F_1 \) plants were tall. No intermediate height or short plants appeared. Observation 1: All \( F_1 \) progeny exhibited only one of the parental traits (the dominant trait) and were uniform.
Step 3: Observation 2 - Absence of the other parental trait.
The trait of the other parent (recessive trait) completely disappeared or remained hidden in the \( F_1 \) generation. In the tall × short cross, the short trait was not seen in any \( F_1 \) plant. \[ \boxed{\text{Observation 2: The recessive parental trait did not appear in any \( F_1 \) plant; it was completely masked.}} \]
Step 4: Additional observations (for reference).
Other observations made by Mendel about \( F_1 \) progeny include:

• All \( F_1 \) plants were hybrids (heterozygous).
• The \( F_1 \) plants showed the dominant trait regardless of whether the dominant allele came from the male or female parent (reciprocal crosses gave same result).
• When \( F_1 \) plants were self-pollinated, the recessive trait reappeared in \( F_2 \) generation in a definite ratio (3:1).

Step 5: Final answer with both observations.
Two observations: (1) All \( F_1 \) progeny showed only the dominant trait and were uniform. (2) The recessive trait completely disappeared in \( F_1 \) generation.