Mechanism of Incomplete Dominance
Generally, genes are present in pairs in an individual, with one copy inherited from each parent. In complete dominance, one allele is fully expressed, masking the effects of the other allele. However, in incomplete dominance, the heterozygous genotype (having two different alleles) results in a phenotype that is a combination or blend of the phenotypes associated with each allele. The mechanism of incomplete dominance is as follows:
The presence of two dominant red alleles is represented by RR, while the presence of two recessive white alleles is denoted by rr. In a test cross between red and white flower-bearing plants, the F1 generation produced pink flowers, so it is evident that the heterozygous individuals (Rr) show an intermediate phenotype. This means that neither allele is completely dominant, and the pink color is a blend of the red and white alleles rather than one allele fully overshadowing the other.
In the F2 generation, when the heterozygotes (Rr) are cross-pollinated to assess their traits, their progeny will exhibit the genotypes RR, Rr, and rr in a ratio of 1:2:1. This means that some individuals will inherit two copies of the dominant R allele, some will inherit two copies of the recessive r allele, and others will inherit both the dominant R and recessive r alleles. This genotypic ratio aligns with the classic Mendelian ratio observed in inheritance.
This clarifies that incoomplete dominance does not mean complete blending, as demonstrated by the fact that half of the F2 progeny still exhibit the parental homozygous alleles. Despite all the offspring in the F1 generation being heterozygous and displaying the intermediate phenotype, the presence of both the dominant and recessive alleles is still evident in the subsequent generation.
Incomplete Dominance & Mendel’s Experiment
Incomplete Dominance is a form of intermediate inheritance where neither of the two alleles for a particular trait is completely dominant over the other. In this type of dominance, the heterozygous phenotype is a blend or intermediate between the two homozygous phenotypes. The concept of incomplete dominance emerged as a significant discovery following Gregor Mendel’s initial work in genetics. Incomplete dominance plays an important role in contributing to the diversity and variation of an organism’s traits or characteristics.
Table of Content
- What is Incomplete Dominance?
- Mechanism of Incomplete Dominance
- Concept of Dominance
- Incomplete Dominance and Codominance
- Examples of Incomplete Dominance
- FAQs on Incomplete Dominance
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