Question

Which case is represented if F2 generation in a Mendelian Cross shows that both genotypic and phenotypic ratios are same as $1:2:1$?

• A. Monohybrid cross with incomplete dominance
• B. Monohybrid cross with complete dominance
• C. Codominance
• D. Dihybrid cross

Answer 1

The correct option is A

Monohybrid cross with incomplete dominance

The correct option is A.

The explanation for correct option:

1. Incomplete dominance is a type of gene interaction in which both alleles of a gene present at a locus are expressed partially, which results in an intermediate or different phenotype.
2. An example of incomplete dominance is the plant Snapdragon.
3. In heterozygous individuals, poor dominance results in a mixing of traits. For instance, all the pink flowers in the F1 generation of snapdragon with the genotype Rr result from a hybrid between homozygous red (RR) and white (rr) color-flowered plants.
4. The F1 plants produce red, pink, and white flowers in the ratio of 1:2:1 when self-pollinated. Here, the ratio of genotype to phenotype is the same.

Explanation for incorrect options:

Option B:

1. Complete dominance is the term used for the type of dominance in which one allele completely masks the effect of the other allele.
2. It is a form of dominance in which the effect of the recessive gene in a heterozygous state is totally concealed by the dominant gene.
3. There are many examples of complete dominance in humans, including having specific hair color, skin pigment, and brown eyes.

Option C:

1. Codominance is the term implied for a type of inheritance in which two alleles of the same gene are expressed separately giving rise to different traits in an individual.
2. An example is ABO blood grouping.
3. ABO blood grouping is controlled by gene I which has three alleles A, B, and O and show codominance.
4. An O allele is recessive to both A and B.
5. The A and B alleles are codominant with each other.

Option D:

1. A Dihybrid cross is a cross between two individuals with two observed traits which are controlled by two different genes.
2. An example of a dihybrid cross is the cross between a homozygous pea plant with round yellow seeds and wrinkled green seeds.
3. Here the two traits are, texture and color of the seeds.

Final answer: F2 generation in a Mendelian cross with both genotypic and phenotypic ratios $1:2:1$is a case of incomplete dominance.