Question

Expression of different genes for different traits may show dominance, incomplete dominance or co-dominance. Write about expression of such genes with the help of one example each.

Answer 1

The expression of distinct genes for specific qualities can display multiple patterns, including dominance, partial dominance, or co-dominance.

1. Dominance: Dominance occurs when one allele totally suppresses the expression of the other in a heterozygous individual. In this scenario, the dominant allele is expressed, while the recessive allele is hidden. For example, Mendel's pea plant experimented with bloom colour. In pea plants, the purple flower allele (P) is dominant over the white flower allele (P). When a plant receives one gene for purple flowers (PP) and one for white flowers (pp), the dominant purple allele suppresses the development of the recessive white allele, resulting in purple blooms.
2. Incomplete Dominance: It is a form of inheritance in which heterozygous progeny exhibit an intermediate phenotype between two parental traits. For instance, the blossom hue in snapdragon (Antirrhinum sp.). The allele for white flowers (r) in snapdragons is partially dominant over the allele for red flowers (R). Pink flowers that combine the colours of red and white are produced when a plant gets one gene for red flowers (RR) and one allele for white flowers (rr).
3. Co-dominance: In a hybrid, it is the inheritance pattern when both alleles of a gene express themselves equally and independently, meaning that both alleles are dominant. Take human ABO blood grouping, for instance. The gene regulates the ABO blood classes. i, I^A, and I^B are the three alleles that are associated with the gene i. However, a person can have any two of these three alleles depending on their genetic makeup. i is a recessive allele, though I^A and I^B are both dominant alleles. i is the only one of the three. While the allele i does not create any antigen, the alleles I^A and I^B result in the production of antigen A and antigen B, respectively, on the surface of the red blood cell. I^A and I^B both express their respective types of surface antigens, A and B, when they are in the same setting together. Because of co-dominance, this is the case.