Here's a breakdown:

* Allele: A variant form of a gene.

* Heterozygous: Having two different alleles for a particular gene.

* Phenotype: The observable characteristics of an organism.

In contrast to simple dominant-recessive inheritance, where one allele completely masks the other, co-dominance results in a blending or combination of both traits.

Example:

A classic example is the ABO blood group system in humans. There are three alleles: A, B, and O.

* A and B alleles are co-dominant. If an individual inherits both A and B alleles (AB genotype), they will have both A and B antigens on their red blood cells, resulting in AB blood type.

* O allele is recessive. If an individual inherits an O allele along with either A or B, the A or B allele will be expressed, resulting in blood type A or B, respectively.

Key Points:

* Both alleles are expressed.

* Neither allele is dominant or recessive.

* The phenotype is a combination of both alleles.

* Results in a "blending" of traits.

Other Examples:

* Roan cattle: Have a mixture of red and white hairs, resulting from co-dominance between red and white coat color alleles.

* Sickle cell anemia: Individuals with one sickle cell allele and one normal allele have a milder form of the disease due to co-dominance.

Understanding co-dominance is crucial for understanding how traits are inherited and expressed in organisms. It helps explain the diversity of phenotypes observed in the natural world.