F2 generation in a Mendelian cross showed that both genotypic and phenotypic ratios are same as 1 : 2 : 1. It represents a case of : [2012]a)Co-dominanceb)Dihybrid crossc)Monohybrid cross with complete dominanced)Monohybrid cross with incomplete dominanceCorrect answer is option 'D'. Can you explain this answer?

Question

Answer

In incomplete dominance both the characters are shown due to the dominance of both allele.

Answer

The incomplete dominance is the exception of first law of Mendle.-:
in this case none of the two alleles able to express themselves in dominant form.
so in hybrid variety a third allele comes into the action so the phenotypic ratio becomes 1:2:1
here -:
1 homozygous dominant
1 homozygous recessive and
2 heterozygous allels are involved

Answer

Monohybrid Cross with Incomplete Dominance

Incomplete dominance occurs when the heterozygous phenotype is an intermediate blend of the two homozygous phenotypes. In this case, the F2 generation of a monohybrid cross showed genotypic and phenotypic ratios of 1 : 2 : 1, which is indicative of incomplete dominance.

Explanation:

1. Monohybrid Cross:
A monohybrid cross involves the study of one trait. In this case, the F2 generation is derived from a cross between two hybrid parents, each carrying two different alleles for a particular trait.

2. Genotypic Ratio:
The genotypic ratio in the F2 generation is 1 : 2 : 1, which means that there are three possible genotypes: homozygous dominant (AA), heterozygous (Aa), and homozygous recessive (aa). Each genotype appears in the F2 generation with a frequency of 1, 2, and 1, respectively.

3. Phenotypic Ratio:
The phenotypic ratio in the F2 generation is also 1 : 2 : 1, which means that there are three possible phenotypes: the dominant phenotype (expressed by homozygous dominant individuals), the intermediate phenotype (expressed by heterozygous individuals), and the recessive phenotype (expressed by homozygous recessive individuals). Each phenotype appears in the F2 generation with a frequency of 1, 2, and 1, respectively.

4. Incomplete Dominance:
The fact that the phenotypic ratio in the F2 generation is not 3 : 1 (as expected in a case of complete dominance) indicates the presence of incomplete dominance. In incomplete dominance, neither allele is completely dominant or recessive, and the heterozygous genotype produces a phenotype that is an intermediate blend of the two homozygous phenotypes.

5. Example:
For example, if we consider a monohybrid cross between red (RR) and white (rr) flower color in snapdragons, the F1 generation will be heterozygous (Rr), and the F2 generation will show a phenotypic ratio of 1 red : 2 pink : 1 white. The pink color is an intermediate blend of red and white, indicating incomplete dominance.

Conclusion:
Based on the genotypic and phenotypic ratios of 1 : 2 : 1 in the F2 generation, it can be concluded that the case represents a monohybrid cross with incomplete dominance.

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