ABO blood groups are controlled by _______.
Gene I
Understanding ABO Blood Groups
ABO blood groups are a classification system for blood types based on the presence or absence of inherited antigenic substances on the surface of red blood cells.
These antigens can be Type A, Type B, both Type A and B, or neither. The body's immune system reacts to the types of antigens present or absent, which is crucial for blood transfusions.
The Gene Controlling ABO Blood Types
The inheritance of ABO blood groups is determined by a single gene. This gene provides the instructions for producing certain enzymes that add specific sugar molecules (antigens) to the surface of red blood cells.
The question asks which gene controls the ABO blood groups. This specific gene is known as Gene I (also sometimes referred to as the ABO gene). Therefore, the ABO blood groups are controlled by Gene I.
Alleles of Gene I
The gene controlling ABO blood groups, Gene I, exists in three different versions, or alleles:
IA: This allele codes for an enzyme that adds N-acetylgalactosamine to the red blood cell surface, resulting in the A antigen.
IB: This allele codes for an enzyme that adds D-galactose to the red blood cell surface, resulting in the B antigen.
i: This allele is recessive and codes for a non-functional enzyme, meaning no sugar molecule is added, and neither A nor B antigen is produced.
Genotypes and Phenotypes of ABO Blood Groups
Since humans inherit one allele from each parent, there are different combinations of these three alleles, leading to various genotypes and resulting phenotypes (blood types). The possible genotypes and their corresponding ABO blood group phenotypes are:
| Genotype | Phenotype (Blood Group) | Antigens on Red Blood Cells |
|---|---|---|
| IAIA | A | A antigen |
| IAi | A | A antigen |
| IBIB | B | B antigen |
| IBi | B | B antigen |
| IAIB | AB | A and B antigens |
| ii | O | Neither A nor B antigen |
Dominance and Codominance in ABO Inheritance
The inheritance pattern of the ABO blood groups involves both dominance and codominance:
The alleles IA and IB are both dominant over the allele i. This is why individuals with genotypes IAi or IBi have phenotypes A and B, respectively.
The alleles IA and IB are codominant with respect to each other. This means that if an individual inherits both IA and IB (genotype IAIB), both antigens (A and B) are produced, resulting in the AB blood group.
Revision Table: ABO Blood Group Genetics
| Concept | Explanation |
|---|---|
| Controlling Gene | Gene I (or ABO gene) |
| Number of Alleles | 3 (IA, IB, i) |
| IA and IB dominance | Dominant over i |
| IA and IB relationship | Codominant |
| Resulting Phenotypes | A, B, AB, O |
Additional Information on Blood Group Inheritance
Understanding ABO blood group inheritance is a classic example in genetics illustrating concepts like multiple alleles and codominance. Beyond the ABO system, other blood group systems exist, such as the Rh system (positive or negative), which are controlled by different genes.
The knowledge of ABO blood groups is critical for safe blood transfusions and understanding inherited traits.
Important Questions from Molecular Basis of Inheritance
Which of the following statements are incorrect with respect to nucleotides?
(A) Purines and pyrimidines are nitrogenous bases.
(B) Nucleotides are non-enzymatic molecules.
(C) Phosphate group is linked to –OH of 5' C of a nucleoside through phosphoester linkage.
(D) In RNA, every nucleotide residue has an additional –OH group present at 2' position in the ribose.
(E) Thymine is an example of pyrimidine.
Arrange the given steps of DNA fingerprinting in the sequence from initiation to end:
(A) Digestion of DNA by restriction endonuclease
(B) Isolation of DNA
(C) Hybridisation using labelled VNTR probe
(D) Transferring (blotting) of separated DNA fragments to synthetic membrane
Nucleosome is associated with _______ molecules of histones.
Two nucleotides linked together to form a dinucleotide through:
Match List-I with List-II:
List-I (Name of the organism) List-II (Chromosome number in a meiocyte) (A) Rat (I) 38 (B) Dog (II) 42 (C) Cat (III) 1260 (D) Ophioglossum (IV) 78 Choose the correct answer from the options given below:
