Question

Assertion: A geneticist crossed two plants, he got 50% tall and 50% dwarf progenies.
Reason: It follows Mendelian law as one of the parent plants might be heterozygous.
A. Both Assertion and Reason are correct and Reason is the correct explanation for the Assertion.
B. Both Assertion and Reason are correct and Reason is not the correct explanation for the Assertion.
C. Assertion is correct but Reason is incorrect.
D. Both Assertion and Reason are incorrect.

Answer 1

Hint:- Gregor Mendel conducted his research over a period of eight years on the common garden pea plant Pisum sativum. Thereafter he represented the results of his experiments together with generalization known as “Mendel’s laws”.

Complete step-by-step solution:- Mendel’s law of dominance
When Mendel crossed a true-breeding red flowered plant with a true breeding white flowered plant, he obtained red colored progeny of the flowers. The white color suppressed and the red color dominated. Mendel called such traits as redness of flowers dominant and their alternatives such as whiteness as recessive. All the seven characters in peas studied by Mendel behaved in this way, one of each pair of contrasting traits appear to be dominant and other recessive.
Since an individual develops from the union of two gametes, it receives a gene for a trait like height from both the parents. The true breeding tall plant is therefore represented by TT (homozygous dominant) and its gametes are T; the true breeding dwarf parent is tt (homozygous recessive) and its gametes are t; and the hybrid zygote will have genotype Tt (heterozygous dominant).
As per the question: If one parent is heterozygous for the tall trait then the genotypes would be Tt (tall) and the genotype of the other parent should be tt (homozygous recessive) to obtain 50% tall and 50% dwarf progenies.
Cross: Parents – Tt (tall) X tt (dwarf)

| t| t
---|---|---
T| Tt| Tt
t| tt| tt

Ratio of progenies- Tt (tall): tt (dwarf)
2:2 = 1:1

Note:- The Mendel’s law of dominance is not a universal law as in many cases the dominance is absent and the hybrid individuals resemble neither parent exactly but are more or less intermediated between the two. This is called incomplete dominance.