Question
Explain the following terms with examples: Incomplete dominance.
✓
Answer
Co-dominance: In Mendel's experiment, trait of F 1 resembles either of the two parents (dominance) and was in between two parents in incomplete dominance. But in the case of co-dominance, F, individual is similar to both the parents and expresses both the alleles (dominant and recessive) independently.
→ One of the good example of co-dominance is different types of Red blood cells that determine the ABO blood grouping in human being.
→ There are found four types of blood groups named-A. B, AB and O in human population which were discovered by Landsteiner (1902).
→ ABO blood groups are controlled by gene 'I'. The Plasma membrane of the RBC has sugar polymer (glycoprotein) protruding from its surface and the gene 'I' governs the synthesis and type of sugar polymer.
→ Gene 'I' exists in three allelic forms IA, IB and i. Alleles IA and IBproduce different types of sugar whereas allele does not produce any sugar.
→ IA and IB are dominant over I. It means that when I and i are present together in an individual, only I expresses itself and when Gamma ^ 0 and i are present only expresses.
→ When I and co-exist, they express their type of sugar independently, this is called co-dominance
→ Since gene 'I has three alleles, there is the possibility of six types of combinations of genotypes for ABO blood grouping in human beings as shown in Table given below:>
Incomplete dominance: Mendel proposed the law of dominance by explaining the concept of dominant and recessive traits based on his experiments but when experiments on pea were repeated using other traits in other plants, it was observed that the trait expressed in F1 generation did not resemble with any of the two parent but had expression in between the two and therefore it shows deviation from law of dominance. It is exception to law of dominance and it is called Incomplete dominance.
When a cross was made between true breeding red flowered (RR) and true breeding white flowered (rr) plants of snapdragon (Antirrhinum sp.) the F1 produced Pink flowered (Rr) plants and when the F, was self-pollinated, F2 resulted in 1 Red (RR): 2 Pink (Rr): 1 white (rr); a genotypic ratio similar to typical monohybrid cross with the difference that phenotypic ratio is also 1:2:1 instead of 3:1.
In this experiment, unit factor R was not completely dominant over r and due to this reason, plant with Rr genotype produced the phenotype pink.
→ One of the good example of co-dominance is different types of Red blood cells that determine the ABO blood grouping in human being.
→ There are found four types of blood groups named-A. B, AB and O in human population which were discovered by Landsteiner (1902).
→ ABO blood groups are controlled by gene 'I'. The Plasma membrane of the RBC has sugar polymer (glycoprotein) protruding from its surface and the gene 'I' governs the synthesis and type of sugar polymer.
→ Gene 'I' exists in three allelic forms IA, IB and i. Alleles IA and IBproduce different types of sugar whereas allele does not produce any sugar.
→ IA and IB are dominant over I. It means that when I and i are present together in an individual, only I expresses itself and when Gamma ^ 0 and i are present only expresses.
→ When I and co-exist, they express their type of sugar independently, this is called co-dominance
→ Since gene 'I has three alleles, there is the possibility of six types of combinations of genotypes for ABO blood grouping in human beings as shown in Table given below:
| Allele from Parent 1 | Allele from Parent 2 | Genotype of offspring | Blood types of offspring |
| IA | IA | IAIA | A |
| IA | IB | IA | AB |
| IA | i | $I ^{ A } i$ | A |
| IB | IA | IAIB | AB |
| IB | IB | IBIB | B |
| IB | i | $I ^{ B } i$ | B |
| i | i | ii | O |
When a cross was made between true breeding red flowered (RR) and true breeding white flowered (rr) plants of snapdragon (Antirrhinum sp.) the F1 produced Pink flowered (Rr) plants and when the F, was self-pollinated, F2 resulted in 1 Red (RR): 2 Pink (Rr): 1 white (rr); a genotypic ratio similar to typical monohybrid cross with the difference that phenotypic ratio is also 1:2:1 instead of 3:1.
In this experiment, unit factor R was not completely dominant over r and due to this reason, plant with Rr genotype produced the phenotype pink.
Need a full question paper?
Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.
Explore more
Similar questions
How does a transgenic organism differ from the rest of its population? Give any two examples of such organism for human advantage.
- Explain the phenomena of multiple alleles and co-dominance taking ABOblood group as an example.
- What is the phenotype of the following:
- IA i
- i i
Somatic chromosome number is 40. What shall be the chromosome number in the cells of seminiferous tubules?
Study the population growth curves in the graph given below and answer the questions which follow:
- Identify the growth curves ‘a’ and ‘b'.
- Which one of them is considered a more realistic one and why?
- If dN/dt=rN(K-N/K) is the equation of the logistic growth curve, what does K stand for?
- What is symbolised by N?
Taking the example of white-winged moths and dark-winged moths of England in pre and postindustrialised era, explain evolution by natural selection.
OR
How can evolution by natural selection be explained by melanised moths before and after industrialisation in England?OR
How did industrialisation play a role in Natural Selection of light and dark-coloured moth in England?OR
Which type of cell division forms spermatids from the secondary spermatocytes?
What is apomixis and what is its importance?
How does a mutagen induce mutation? Explain with example.
How is biodiversity important for ecosystem functioning?
A non–haemophilic couple was informed by their doctor that there is possibility of a haemophilic child be born to them. Explain the basis on which the doctor conveyed this information. Give the genotypes and the phenotypes of all the possible children who could be born to them.