Question

Mendel worked out the rules of heredity by working on garden pea using a number of visible contrasting characters. He conducted several experiments by making a cross with one or two pairs of contrasting characters of pea plant. On the basis of his observations he gave some interpretations which helped to study the mechanism of inheritance.
(i) When Mendel crossed pea plants with pure tall and pure short characteristics to produce F₁ progeny, which two observations were made by him in F₁ plants?
(ii) Write one difference between dominant and recessive trait.
(iii) (A) In a cross with two pairs of contrasting characters
                   RRYY × rryy
      (Round Yellow)   (Wrinkled Green)
Mendel observed 4 types of combinations in F₂ generation. By which method did he obtain F₂ generation? Write the ratio of the parental combinations obtained and what conclusions were drawn from this experiment.

OR

(iii) (B) Justify the statement :
“It is possible that a trait is inherited but may not be expressed.”

Answer 1

(i) • All F1 plants were tall, showing that tallness is a dominant trait.
  • The short (recessive) trait was not expressed in the F1 generation.

(ii) • Dominant Trait: Expressed in the presence of both homozygous and heterozygous alleles.
      • Recessive Trait: Expressed only in the homozygous condition.

(iii)A • Method: Self-pollination of F1 progeny (RrYy).
         • F2 Generation Phenotypic Ratio: 9 (Round Yellow): 3 (Round Green): 3 (Wrinkled Yellow): 1 (Wrinkled Green).
         • Conclusions: Traits segregate independently, demonstrating the Law of Independent Assortment.

(iii)B  A trait can be inherited but not expressed if it is recessive and the individual possesses a dominant allele for that trait. In heterozygous conditions, the dominant trait masks the recessive trait, making it unexpressed but still inheritable.