Intermediate Inheritance: Definition, Explanation, and Examples

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 1. Definition of Intermediate Inheritance

When neither allele is entirely dominant over the other, the result is an intermediate phenotype in the heterozygous state. This is known as intermediate inheritance.

Simply:

When the phenotype (appearance) of the offspring combines or blends the two parental traits, this is known as intermediate inheritance.

One of the main forms of non-Mendelian inheritance, incomplete dominance, is another name for this pattern.

2. Explanation

One dominant allele totally obscures the effect of the recessive allele in Mendelian inheritance.
On the other hand, both alleles partially contribute to the phenotype in intermediate inheritance.

As a result, the heterozygous person exhibits a phenotype that is between that of their two homozygous parents.

For instance:

✔ The F₁ offspring (Rr) of a cross between a red-flowered plant (RR) and a white-flowered plant (rr) have pink flowers.

✔ The color pink is between red and white.

As a result, neither red nor white fully dominates; both have an impact on the result.

3. Genetic Basis of Intermediate Inheritance

Partial dominance of alleles at a specific gene locus is the fundamental cause of intermediate inheritance.

✔ The phenotype is influenced to some degree by each allele.

✔  While the heterozygote produces more than the recessive homozygote, it produces less gene product (protein or pigment) than the dominant homozygote.

The phenotype is therefore in the middle of the two extremes.

Ratios of genotype and phenotype (F₂ Generation):

The F₂ generation exhibits the following if the intermediate form F₁ heterozygotes self-pollinate:

✔ The genotypic ratio is 1 2 1.

✔ The phenotypic ratio is 1 (parent 1) to 2 (intermediate) to 1 (parent 2).

An illustration of flower color (Mirabilis jalapa):

Genotype Phenotype
RR Red flowers
Rr Pink flowers (intermediate)
rr White flowers

4. Examples of Intermediate Inheritance

a. In Plants

  1. Mirabilis jalapa (Four-o’clock plant):

    • Red × White → Pink flowers in F₁.

    • Classic example of incomplete dominance.

  2. Snapdragon (Antirrhinum majus):

    • Red × White → Pink flowers.

  3. Wheat kernel color:

    • Red × White → Intermediate (light red) kernels.

b. In Animals

  1. Andalusian fowl (chickens):

    • Black × White → Blue or gray offspring.

  2. Cattle coat color:

    • Red × White → Roan (a mixture of red and white hairs).

c. In Humans

  • Wavy hair results from a cross between curly-haired and straight-haired parents.

5. Difference Between Intermediate Inheritance and Complete Dominance

Feature Complete Dominance Intermediate Inheritance (Incomplete Dominance)
Dominance Type One allele completely masks the other Neither allele completely dominates
Heterozygote Phenotype Same as a dominant homozygote Intermediate between both parents
Example Tall (Tt) pea plants are tall Pink flowers in Mirabilis jalapa
Phenotypic Ratio (F₂) 3:1 1:2:1

6. Molecular Basis of Intermediate Inheritance

Incomplete dominance at the molecular level happens when:

✔ To fully express the dominant phenotype, the dominant allele is unable to produce enough of the gene product (protein or pigment).

✔ An intermediate expression results from the heterozygote producing half as much of the functional product.

For instance, the pigment anthocyanin is responsible for the red hue of Mirabilis jalapa.

✔ Red pigment is produced in large quantities by RR plants.

✔ White plants don't produce anything.

✔ Half (pink) is produced by Rr plants.

The intermediate color is thus explained by pigment concentration.

7. Importance in Plant Breeding and Genetics

It is essential to comprehend intermediate inheritance in:

A. Estimating the performance of hybrids and choosing appealing combinations.

B. Elucidating quantitative characteristics where partial dominance is prevalent, like height, grain color, or yield.

C. Creating breeding plans that make use of intermediate phenotypes to enhance quality traits (e.g., medium maturity, moderate plant height).

D. Since it shows that not all traits adhere to Mendel's rigid dominance patterns, genetic studies and education are important.

8. Summary

✔ A blended phenotype is the result of intermediate inheritance, also known as incomplete dominance, where both alleles express themselves partially.

✔ Complete dominance, in which one allele obscures the other, is not the same as this.

✔ Both genotype and phenotype exhibit a 1:2:1 ratio in the F₂ generation.

✔ Humans, animals, and plants all have it.

It is crucial to current studies in plant breeding and genetics.

To put it briefly:
A mixed or intermediate trait in the progeny results from intermediate inheritance, which is the partial expression of both alleles.

Keywords: intermediate inheritance definition, incomplete dominance, examples of intermediate inheritance, Mendelian vs non-Mendelian inheritance, incomplete dominance in plants, intermediate inheritance in animals

(Note: The article was created by ChatGPT; however, conceptualization, review, and editing of this article were done by Dr. UKS Kushwaha.)







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