Question

Define – Incomplete Dominance.

Hint:

In incomplete dominance, the heterozygous offspring exhibit an intermediate phenotype, which results in a 1:2:1 phenotypic ratio in the F2 generation.

Answer 1

Step 1: Understanding Incomplete Dominance.
Incomplete dominance occurs when the heterozygous genotype produces an intermediate phenotype that is a blend of the two homozygous phenotypes. In this case, neither allele is completely dominant over the other.
Step 2: Example.
For example, in the case of flower color in Mirabilis jalapa, where red (R) is incompletely dominant over white (W), the F1 generation from a cross between red and white flowers would have pink flowers (RW).
Step 3: Conclusion.
Incomplete dominance results in a blending of traits in the heterozygous individuals, rather than one allele completely masking the effect of the other.
ii. If a red-flowered Mirabilis jalapa plant is crossed with a white-flowered plant, what will be the phenotypic ratio in F2 generation? Show it by a chart.
Solution:
Step 1: Understanding the genetic basis.
In the case of incomplete dominance, the red-flowered plant (RR) is crossed with a white-flowered plant (WW). The F1 generation will all be heterozygous (RW), resulting in pink flowers. In the F2 generation, the offspring will inherit alleles from both parents. The cross for F2 will be: \[ \text{F1 Cross:} \, RW \times RW \] Step 2: Punnett square for F2 generation.
\[ \begin{array}{c|c c} & R & W
\hline R & RR & RW
W & RW & WW
\end{array} \] Step 3: Phenotypic Ratio.
- Red flowers (RR): 1
- Pink flowers (RW): 2
- White flowers (WW): 1
Step 4: Conclusion.
The phenotypic ratio in the F2 generation is 1 red: 2 pink: 1 white.