The concept depicted by a cross in which the phenotype of F₁ generation expresses both the parents to some degree is:

Correct option is D

The concept depicted by a cross in which the F₁ generation expresses both the parents to some degree is co-dominance. 

Explanation: Co-dominance means that both alleles of a gene pair are expressed equally in the phenotype of the offspring, resulting in a blend of the parental traits. 

Why other options are incorrect:

• Incomplete dominance: 

In incomplete dominance, the F₁ generation exhibits a phenotype that is intermediate between the parental phenotypes, not a full expression of both. 

• Law of dominance: 

The law of dominance states that in a heterozygous individual, the phenotype of the dominant allele is expressed, while the recessive allele is masked. This does not represent a blending of parental traits. 

• Inheritance of one gene: 

Inheritance of one gene refers to the transmission of a single gene from parents to offspring. This concept doesn't necessarily explain the phenotypic outcome in the F₁ generation.