List all possible genotypes for the A, B, AB, and O phenotypes. Is the mode of inheritance of the ABO blood types representative of dominance, recessiveness, or codominance?

Verified step by step guidance

1. Understand that the ABO blood group system is determined by the presence of antigens on the surface of red blood cells, which are controlled by the ABO gene.
2. Identify the alleles involved: A, B, and O. The A and B alleles are codominant, meaning both can be expressed simultaneously, while the O allele is recessive.
3. List the possible genotypes for each phenotype: A phenotype can be IAIA or IAi, B phenotype can be IBIB or IBi, AB phenotype can only be IAIB, and O phenotype can only be ii.
4. Recognize that the mode of inheritance for the ABO blood types is an example of codominance, as both A and B alleles can be expressed together in the AB phenotype.
5. Note that the O phenotype is an example of recessiveness, as it only appears when both alleles are the recessive i allele.

Key Concepts

ABO Blood Group System

The ABO blood group system classifies human blood into four main phenotypes: A, B, AB, and O, based on the presence or absence of antigens on the surface of red blood cells. The A and B alleles are responsible for the A and B antigens, while the O allele does not produce any antigens. Understanding this system is crucial for determining the possible genotypes associated with each phenotype.

Genotypes and Phenotypes

A genotype refers to the genetic constitution of an individual, while a phenotype is the observable expression of that genotype. For the ABO blood types, the possible genotypes include AA, AO (for phenotype A), BB, BO (for phenotype B), AB (for phenotype AB), and OO (for phenotype O). Recognizing the relationship between genotypes and phenotypes is essential for listing all possible genotypes for the given blood types.

Codominance

Codominance is a form of inheritance where both alleles in a heterozygous individual contribute equally and visibly to the phenotype. In the case of the ABO blood types, the A and B alleles are codominant, meaning that individuals with genotype AB express both A and B antigens. This concept is key to understanding the inheritance pattern of the ABO blood group system, distinguishing it from simple dominance and recessiveness.