Question

Choose the correct answer from the alternatives given.
Fruit shape in shephereds 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 $\times$ tt	All triangular
Strain 2 $\times$ tt	1 triangular : 1 top-shaped
Strain 3 $\times$ tt	All top-shaped
Strain 4 $\times$ tt	3 triangular :1 top-shaped

Which pair of strains possess the genotype Tt?

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

Answer 1

Answer: (B)

Strains 2 and 4

The strain 2 that has one triangular and one top shaped fruit will have the genotype 'Tt' which is heterozygous and results hence with a cross recessive genotype 'tt' two genotype the 'Tt' and 'tt' that will give the triangular and top-shaped fruit respectively. The strain 4 also has heterozygous 'Tt' genotype and will give with the cross of 'tt' 3 heterozygous and one recessive genotype and hence 3 triangular and 1 top shaped fruit.

So, the correct answer is ' Strains 2 and 4'.