Question

Which of the following conditions represents a case of co-dominant genes?
A. A gene expresses itself, suppressing the phenotypic effect of its alleles
B. Genes that are similar in phenotypic effect when present separately, but when together interact to produce a different trait
C. Alleles, both of which interact to produce a trait, which may or may not resemble either of the parental types
D. Alleles, each of which produces an independent effect in a heterozygous condition

Answer 1

In genetics, co-dominance refers to a phenomenon occurring in an organism where the degree of expression of the two alleles is equal. Moreover, the trait that results from the crossing over of two alleles expressing equally and independently is known as the co-dominant trait.

Complete answer:
The relations among the two versions of a gene can be depicted as codominance. When crossing over takes place between the alleles of two traits, the offspring in F1 generation receives one alternative form of a gene known as allele from each of the parents. In case of different alleles, usually the allele which is dominant is expressed while the recessive one is often masked. But in case of codominance, no recessive allele is there; both the alleles independently express their phenotypes even in heterozygous state.
In other words, the co-dominant gene does not show any intermediate condition or dominant-recessive correlation. In-fact, both alleles are expressed equally. This condition can be easily seen in many animal and plant species having more than one pigment color. Flowers having petals of different color and the black and white spotted cows are the common examples of codominance.

Hence, the correct answer is option (D).

Note: Alleles of a pair of genes are fully expressed in a heterozygous condition. This condition is referred to as co-dominance which is a kind of inheritance. AB type of blood group is an example of codominant trait. Individuals having AB blood group have allele A from one parent while allele B from another parent. This blood group expresses both antigen A and B equally therefore the alleles A and B are said to be codominant.