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

t t
t tt tt
t tt tt t = tall height
t = short height

part a: identify the genotype course & phenotypic ratios of the offspring.

part b: identify two offspring from the punnet square that could produce short pea plants if they were crossed. explain your answer.

Answer

Part a

50% TT, 50% Tt, 100% tall

Part b

Tt x Tt

Explanation:

Part a

The cross is between a homozygous tall pea plant (TT) and a heterozygous tall pea plant (Tt). This produces 2 genotypes at a ratio of 1:1 TT, and Tt. In other words, 50% TT and 50% Tt. These are the same as the parental genotypes, and it means that 100% of the offspring will be tall. (as T  (tall) is the dominant allele.

Part b

A cross between the two heterozygous plants would give the following punnett square:

  T   t

T TT Tt

t Tt   tt

The genotype ratios are 1 TT: 2 Tt: 1 tt, in other words, 25% TT, 50% Tt, and 25% tt. The resulting phenotypes would therefore be 3 tall (TT + Tt): 1 short (tt), or 75% tall, 25% short. This therefore produces some short plants, at a ratio of 25%.

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