The correct answer is (a) tallness is the dominant trait.
Explanation:
Dominant trait:
When a pea plant has both the allele for tallness (T) and the allele for shortness (t), the tallness allele (T) is considered dominant, meaning it is the trait that is expressed in the phenotype.
Recessive trait:
The shortness allele (t) is recessive, meaning it is only expressed when the individual has two copies of the t allele (tt).
Why other options are incorrect:
(b) Shortness is the dominant trait:
This is incorrect because the results of the cross show that tallness is dominant. If shortness were dominant, all offspring would be short, not tall.
(c) Tallness is the recessive trait:
This is incorrect. A recessive trait only shows up when both alleles are recessive. In this case, the offspring are all tall, indicating that tallness is dominant. Since the offspring are all tall, even though they are heterozygous (Tt), the tall allele (T) is dominant over the short allele (t).
(d) Height of pea plant is not governed by gene ‘T’ or ‘t’:
This is incorrect. The question is specifically about the inheritance pattern of tallness and shortness in pea plants, which is well-established to be governed by the genes T and t.