Blood type is an example of neither one may be dominant over the other, in which two alleles may be expressed, but:
– heterozygosity
– independent assortment
– co-dominance
– incomplete dominance
The correct answer and explanation is:
The correct answer is co-dominance.
Co-dominance occurs when both alleles contribute equally and visibly to the organism’s phenotype. This means that in the case of blood types, both the A allele and the B allele are expressed equally in individuals with AB blood type. Unlike typical dominant-recessive relationships, where one allele masks the expression of the other, co-dominant alleles are both observable. For example, someone with type AB blood has both the A and B antigens on their red blood cells.
In a typical dominance relationship, one allele can mask the expression of the other. For instance, if a person inherits a dominant allele for a particular trait and a recessive allele, the dominant allele will determine the phenotype. In the case of incomplete dominance, the heterozygous individual expresses a blended phenotype, where neither allele is fully dominant, leading to a third, intermediate phenotype. However, in co-dominance, the presence of both alleles is fully expressed without blending. For instance, in the AB blood type, the person will express both the A and the B antigens distinctly, not a mixture of the two.
Independent assortment refers to how genes for different traits segregate independently from one another during the formation of gametes, which is not directly related to the expression of co-dominant alleles. Heterozygosity simply refers to an individual possessing two different alleles for a gene, but this alone does not explain the simultaneous expression of both alleles as seen in co-dominance.
Co-dominance is a critical concept in understanding genetic inheritance, especially for traits like blood type, where both alleles can contribute to the phenotype without one overshadowing the other.