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The Punnett square below shows a cross between a pure tall and heterozygous tall plant. What is the total number of tall offspring represented in the Punnett square?
T- tall plant
t- short plant
Gametes T T
T TT TT
t Tt Tt

A. None are short
B. 25% are short
C. 50% are short
D. 75% are short

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Last updated date: 27th Feb 2024
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IVSAT 2024
Answer
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Hint: The offsprings produced would be either heterozygous dominant or homozygous dominant.

Complete answer: A pure tall plant has the genotype TT and the heterozygous tall plant has the Tt genotype.
We know that, T is dominant and t is recessive. It means ‘T’ allele (tall) dominates over ‘t’ (short).
Cross is shown between a pure tall (TT) and heterozygous tall plant (Tt) would produce:
GametesTT
TTT(tall)TT(tall)
tTt(tall)Tt(tall)

Hence, the phenotypic ratio of TT : Tt = 1 : 1
The phenotype shows that TT & Tt both are tall plants and there are no short plants.

So, the correct answer is A. None are short

Note: The above cross is a monohybrid cross. A monohybrid cross is the one which takes place between two individuals with different alleles of a single genetic locus.