Which option below best illustrates a heritable quantitative trait?

a. phenotype only affected by a single gene with a dominant and recessive allele.
b. continuous variation in a phenotype, with offspring that resemble their parents.
c. discrete phenotypic classes. variation in a trait that is determined only by environment.
d. crossing extreme phenotypes produces a phenotypic ratio of 9: 3: 3: 1 in the offspring.

The correct answer is B. Continuous variation in a phenotype, with offspring that resemble their parents.

Explanation:

A heritable quantitative trait is a phenotype that can be measured and depends on the total actions of various genes, and the environmental conditions. Such traits can be different among different individuals, over a range, to generate a continuous proportion of phenotypes.

In a continuous variation, each value of the phenotype is following up to the value of before.

Thus, the correct answer is option B.