Question

Which of the following conditions represents a case of codominant genes?
a. A gene expresses itself , suppressing the phenotypic effect of it’s 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 if the parental types
d. Alleles, each of which produces an independent effect in a heterozygous condition.

Answer 1

Hint: The fundamental physical and functional unit of heredity is a gene. The genes consist of DNA. Some genes serve as instructions for creating protein-called molecules. Many genes do not code for proteins, however. In humans, from a few hundred DNA bases to more than million bases, genes range in size. An international project in study named the Human Genome.

Complete answer:
Every individual has two copies of each gene, one inherited from each parent. In all humans, most genes are the same, although a small number of genes are slightly different between humans. In their sequence of DNA bases, alleles are variants of the same gene with minor variations. These small distinctions contribute to the distinctive physical characteristics of each individual.

Codominance is a relation between a gene's two versions. Individuals obtain from each parent one variant of a gene, called an allele. The dominant allele will usually be displayed if the alleles are different, while the influence of the other allele, called the recessive allele, is masked. However, neither allele is recessive in codominance, and the phenotypes of both alleles are expressed. It is a phenomenon when a gene's two alleles do not have a dominant-recessive relationship or an intermediate condition, but both express themselves in the heterozygous condition independently. This was reported in the colour of the roan coat of cattle. It implies that the presence of the other allele can not be masked by any allele. The ABO blood group, where alleles A and alleles B are both expressed, will be an example in humans. So they have blood type AB if a person inherits allele A from their mother and allele B from their father.

Hence, the correct answer is option (D).

Note: Each of two or more copies of a gene is an allele. For each gene, a human inherits two alleles, one from each parent. When the two alleles are the same, for that gene, the person is homozygous. The person is heterozygous if the alleles are different.