Question

12. The Punnet square below represents the result of the cross between two tall pea plants.

Answer 1

Answers:

Part A:

• Genotypic ratio of offspring is 1:1 (50% homozygous tall and 50% heterozygous tall)
• Phenotypic ratio of the offspring is 100% or all tall.  

Part B:

• if two heterozygous tall plants (Tt) were crossed will produce dwarf plant in the ratio of tall plants to dwarf plants 3:1 (3 tall and 1 dwarf).            

Answer 2

Answer:

Part A

Genotypic ratio---->TT:tt =  1:1 ( TT- 50% and Tt - 50%)

Phenotpyic ratio-----> Tall plants:short plants = 1:0 (Tall plants = 100%)

Part B

Offsprings with genotype Tt will produce short pea plants if they were crossed.

Explanation :

Part A

• The genotypic ratio is the ratio of the various genotypes that appear as a result of a cross. Since in the given cross TT appears 2 times and Tt also appears 2 times, their ratio is 1:1.

• The phenotypic ratio is the ratio of the various phenotypes (the observed traits) seen as a result of a cross. Since T is dominant over t, both TT and Tt genotypes will produce tall plants (phenotype).  So the ratio of tall: short plants will be 1:0.

Part b

For, short pea plants to be produced, it is necessary to take Tt and Tt offsprings because t is a recessive allele and can only express itself in homozygous condition. This condition is only possible on crossing Tt and Tt offsprings.

The result of this cross would be :

Tt X Tt --------> TT Tt Tt tt

Out of these 4 offsprings, the one with genotype tt will be a short plant.