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Genes are divided into alleles, which are distinct variants of the same gene. For each gene, there are two alleles in most of the cases. Codominance occurs when both alleles in a heterozygous state are expressed equally and appear in the phenotype, resulting in a phenotype that is neither dominant nor recessive and Multiple allelism is a situation in which a single phenotypic is represented by multiple alleles rather than two. Incomplete dominance is a phenotypic "blending" of two characteristics, showing that none of the trait is dominant above other.
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Key Terms: Co dominance, multiple alleles, Multiple genes, Codominance traits, Codominance genes, Alleles, Chromosome, Dominance
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Dominance
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Dominance refers to the occurrence of one gene variant on one copy of a chromosome concealing or overcoming the influence of another gene variant on the other chromosome copy. The dominant genotype is dominant, whereas the recessive genotype is recessive. A mutation in one gene, either new or inherited, causes this situation of having two distinct forms of the same gene on each chromosome.
Check Important Notes for Principles of Inheritance and Variation
Codominance
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In one phenotypic, codominance is the manifestation of both alleles' effects separately. It's a non-Mendelian inheritance type that involves a link between alleles of a gene that's equivalent to a dominance relationship. Both alleles are completely expressed in the heterozygous condition, and each allele has its influence on the child.
In codominance, neither allele inhibits the influence of the other. As a result, neither the dominant nor recessive phenotype exists. Instead, it is made up of a mix of the two characteristics. Without combining the separate effects, both alleles exhibit the phenotype with its impact. When the codominance condition exists, the impacts of both alleles may be readily differentiated in the final phenotype. Furthermore, codominance has no quantitative effect.
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Codominance in Human Blood Types
At the population level, there may be three or more alleles for one characteristic.Three distinct alleles in humans can result in four different phenotypes or characteristics. A, B, and O are the alleles, whereas A, B, AB, and O are the phenotypes.
- A blood group is found and distinguished with the type of carbohydrate that is present on the surface of a red blood cell.
- If a person’s red blood cells are coated with carbohydrates A type, then their blood group will be A whereas If it’s coated with carbohydrate B-type then the blood group of that person will be B.
- And the last one is AB which forms when the red blood cell is coated with carbohydrates and proteins.
- Finally, they may contain red blood cells with no carbohydrate coating, indicating that their blood type is O.
- There is a variety of blood group combinations because we receive one blood cell or type from each parent.
- If a person receives A from each parent, then phenotype is A and genotype is AA whereas receiving B alleles from both parents then the phenotype is B and the genotype is BB.
- But things become tricky since both the A and B alleles are dominant, which means they decide the phenotypic of an organism.
- Since both A & B are dominant, if you inherit one A & one B allele from each parent, your blood type and genotype will be AB.
- If both the alleles are expressed shown in the phenotype, it will be a case of codominance.
- What's cooler is that the O allele is recessive, which means it's genetic information that doesn't alter an organism's phenotype until two of those alleles are present.
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| Mendelian Inheritance | Tissue culture | Chromosomal Theory of Inheritance |
Multiple Alleles
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Multiple alleles are a form of non-Mendelian or confused inheritance pattern in which there are more than the normal two alleles that make a typical code for a species' trait.
- When more than two phenotypes are accessible then multiple alleles are present, depending on the dominant or recessive genes present in the trait as well as the dominance pattern the individual genes follow when combined.
- Only simple or full dominance characteristics were tested in Gregor Mendel's pea plants, and there were only two alleles that might contribute to anyone feature the plant displayed.
- It wasn't until later some scientists realized that some qualities might have many alleles that code for different phenotypes.
- This made it possible to see many more phenotypes for any given characteristic while yet adhering to Mendel's Laws of Inheritance.
- When numerous alleles are involved in a characteristic, a variety of dominance patterns might emerge.
- When one of the genes is entirely recessive to all the others, other genes may be co-dominant and exhibit their qualities equally in the individual's phenotype.
- When alleles are combined in a genotype, there are various circumstances where incomplete dominance occurs.
- An individual with this sort of inheritance linked to several alleles would have a blended phenotype, which combines the features of both alleles.
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| Genotype | Blood Type |
|---|---|
| IAIA | A |
| IAIB | AB |
| IAi | A |
| IBIB | B |
| IBi | B |
| ii | O |
Things to Remember
- Co-dominance is a type of dominance in which the kids are genetically identical to both parents due to the mixing of genes.
- Codominance is intimately connected to incomplete dominance, which occurs when both alleles or genes are expressed in the heterozygote at the same time.
- There are numerous conceivable dominance relationships when there are several alleles.
- A dominant trait is manifested in a phenotype, whereas a recessive trait is repressed.
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Sample Questions
Ques. Write the 3 examples of codominance? (3 Marks)
Ans. The following are examples of codominance.
- AB Blood type - A person who has blood group A or B type is expressed by codominance.
- Sickle-Cell Anemia - This is a type of disease that occurs due to codominance.
- Horse colour - Codominance is the reason behind a horse's roan coat colour.
Ques. What is the Difference Between Codominance and Multiple Alleles? (2 Marks)
Ans. When two alleles of a gene contribute to the same characteristic and both contributions can be seen, this is known as codominance. Many alleles play a role in one character in numerous alleles. Multiple alleles: Multiple alleles refer to the presence of one or more alleles in a gene. The best example for multiple alleges is the ABO human blood group.
Ques. Define sickle cell anaemia with the help of codominance? (2 Marks)
Ans. Sickle cell anaemia is a condition in which the red blood cells thin down and stretch out. Half of a person's red blood cells become irregularly shaped if they have a single copy of the sickle-cell allele. When this happens, codominance arises because the blood contains both normal and sickled forms.
Ques. Explain horse roan colour with codominance? (2 Marks)
Ans. The reason behind a horse's roan coat colour is codominance. When a colour is conjugated with white, the outcome is roan. It is the greying of colour, and there are 3 different types of roans in horses: red, bay, & blue. All the shades have similar patterns of co-dominance.
Ques. What are the Similarities Between Codominance and Multiple Alleles? (2 Marks)
Ans. The following are the similarities of codominance and multiple alleles.
- The blood group system of ABO in humans have various alleles & codominance.
- Mendelian inheritance does not apply to Both case of multiple alleles or codominance.
Ques. Define co-dominance & multiple alleles? (5 Marks)
Ans. A link between two variants of a gene is known as codominance. Each parent gives each child one allele, which is a variant of a gene. If the alleles are different, the dominant allele will normally be manifested, while the recessive allele's influence will be muted.
When there are several versions of a gene existing in a population, many alleles exist. Each organism can express two alleles at the same time in creatures with two copies of ever often known as diploid organisms. They might have the same gene or allele, which is known as a homozygous genotype. A heterozygous genotype, on the other hand, might be made up of alleles of multiple kinds. Even though haploid organisms and cells only have one copy of a gene, the population might contain a large number of alleles.
Ques. Give an example of a multiple allele situation.? (3 Marks)
Ans. There are four common alleles in the C gene: C, Cch, ch, and C:
- The fur of a CC rabbit is black and brown.
- The colour of a CHH CHH rabbit is chinchilla-like.
- With a white body and black ears, face, paws, and tail, a ch rabbit shows Himalayan (colour-point) patterning.
- A cc rabbit has a pure white coat and is albino.
Ques. What happens when alleles have codominance? (2 Marks)
Ans. In a heterozygote condition, codominance is an inheritance in which both genes or alleles pairs are completely expressed. As a result, the offspring's phenotype is a blend of the parents' phenotypes. As a result, the characteristic isn't dominant or recessive.
Ques. What are multiple alleles give an example? (2 Marks)
Ans. The ABO blood type system gene and the human-leukocyte-associated antigen (HLA) genes are two examples of multiple-allele genes in humans. 3 alleles represent IA, IB, & IO where I stand for isohaemagglutinin, the ABO system is regulated in humans.
Ques. Is multiple alleles the same as codominance? (3 Marks)
Ans. The main distinction between codominance and multiple alleles is that codominance expresses the effects of both alleles separately in the heterozygous state, whereas multiple alleles refer to the condition of a character with more than two alleles.
Ques. Define co-dominance. (5 Marks)
Ans. Codominance is a type of dominance in which the kids are genetically identical to both parents. Codominance occurs when both parental characteristics are present in the F1 generation. Both parents' genes will be present in the baby. the most basic and common examples of codominance are the ABO blood group. Red blood cells come in a variety of shapes and sizes, including A, B, AB, and O, with or without the rhesus factor. The distinction lies in the antigen found on the surface of red blood corpuscles, which defines an organism's particular blood type. As like, if a person has blood type A, it signifies that antigen-A is present on the RBC surface. However, a gene I am frequently the deciding factor. There are 3 types of alleles in the gene I: IA, IB & i. The alleles IA and IB create two distinct antigens, but the allele-i produces none. As a result, allele I dominate alleles IA and IB.
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