Fruit shape in shephered purse (Capsella bursa) is of two types-triangular and top-shaped. Triangular fruit shape (T) is dominant over top-shape (t). Following table summarises the results of several crosses.
`{:("Cross","Result"),("Strain 1" xx "tt","All triangular"),("Strain 2" xx "tt","1 triangular : 1 top-shaped"),("strain 3"xx "tt","All top-shaped"),("Strain 4"xx "Tt","3 triangular : 1 top-shaped"):}`
Which pair of strains possess the genotyoe Tt ?

Options

A. Strains 2 and 3
B. Strain 2 and 4
C. Strains 1 and 3
D. Strains 1 and 4

Answer

To determine which pair of strains possess the genotype Tt (triangular fruit shape), we can analyze the results of the crosses provided in the table. Let's go through the information step by step.

### Step 1: Understanding the Dominance
- Triangular fruit shape (T) is dominant over top-shaped (t).
- Therefore, Tt or TT will result in a triangular fruit shape, while tt will result in a top-shaped fruit.

### Step 2: Analyzing the Crosses
- **Strain 1 (xx tt)**: All triangular fruits. This indicates that the other parent must be TT (homozygous dominant). Therefore, the genotype is TT x tt.
- **Strain 2 (xx tt)**: Results in a 1:1 ratio of triangular to top-shaped fruits. This indicates a cross between Tt (heterozygous) and tt (homozygous recessive). Therefore, the genotype is Tt x tt.
- **Strain 3 (xx tt)**: All top-shaped fruits. This indicates that both parents must be tt (homozygous recessive). Therefore, the genotype is tt x tt.
- **Strain 4 (xx Tt)**: Results in a 3:1 ratio of triangular to top-shaped fruits. This indicates a cross between Tt (heterozygous) and Tt (heterozygous). Therefore, the genotype is Tt x Tt.

### Step 3: Identifying the Genotype Tt
From the analysis:
- Strain 2 has the genotype Tt (triangular) crossed with tt (top-shaped).
- Strain 4 has the genotype Tt (triangular) crossed with Tt (triangular).

Thus, the pair of strains that possess the genotype Tt is **Strain 2 and Strain 4**.

### Final Answer
The correct pair of strains that possess the genotype Tt is **Strain 2 and Strain 4**.

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