Question
Question: The Punnett square below shows a cross between a pure tall and heterozygous tall plant. What is the ...
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
Solution
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:
| Gametes | T | T |
|---|---|---|
| T | TT(tall) | TT(tall) |
| t | Tt(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.