Question

In a cross between a pea plant heterozygous for round seeds (Rr) and a plant with wrinkled seeds (rr), what is the expected phenotypic ratio of the offspring?

• A. 1 Round : 1 Wrinkled
• B. 3 Round : 1 Wrinkled
• C. All Round
• D. All Wrinkled

Hint:

In a monohybrid cross involving a heterozygous parent (Rr) and a homozygous recessive parent (rr), the phenotypic ratio is always 1:1, as half the offspring inherit the dominant allele and half inherit the recessive allele.

Answer 1

The Correct Option is A

In pea plants, the allele for round seeds (R) is dominant, while the allele for wrinkled seeds (r) is recessive. The cross is between a heterozygous plant (Rr) and a homozygous recessive plant (rr). To determine the phenotypic ratio of the offspring, we use a Punnett square.
The genotypes of the parents are:
- Rr (heterozygous, round seeds), which produces gametes R and r,
- rr (homozygous recessive, wrinkled seeds), which produces only r gametes.
The Punnett square for the cross Rr × rr is:
\[ \begin{array}{c|cc} & R & r
\hline r & Rr & rr
\end{array} \] The offspring genotypes are:
- Rr (round seeds, as R is dominant): 50%,
- rr (wrinkled seeds): 50%.
Thus, the phenotypic ratio is 1 Round : 1 Wrinkled (1:1).