Exemplar Problems

Question:

Explain the following terms with examples:

(a) Co-dominance:

(b) Incomplete dominance:

Answer:

(a) Co-dominance is a genetic phenomenon where two different alleles at a gene locus are both fully expressed in a heterozygous individual. This means that neither allele is dominant or recessive, and they both contribute to the phenotype.

 Example: In the ABO blood group system, individuals with AB blood type have both A and B antigens expressed on their red blood cells, demonstrating co-dominance.

(b) Incomplete dominance is a genetic phenomenon where the heterozygous phenotype is an intermediate or blended expression of the two homozygous phenotypes. Neither allele is completely dominant or recessive.

 Example: In snapdragons, a red-flowered (RR) plant crossed with a white-flowered (WW) plant results in pink-flowered (RW) offspring, showing incomplete dominance.