Which of the following best defines quantitative traits in crops?

Quantitative traits in crops are best defined as measurable traits influenced by multiple genes. These traits, also known as polygenic traits, typically exhibit continuous variation rather than discrete categories, meaning they can be influenced by the interplay of several genetic factors as well as environmental conditions.

For example, characteristics like plant height, yield, and disease resistance are quantitative traits because they aren't controlled by a single gene but by many genes, each contributing a small effect to the overall phenotype. This genetic complexity allows for a range of phenotypic expressions, as seen in a population where individuals can show varying degrees of a certain trait.

While other options refer to gene control or traits, they do not capture the essence of quantitative traits well. Traits controlled by a single gene signify simple inheritance patterns and often result in clear-cut variations, while traits unaffected by the environment neglect the significant impact environmental factors can have on the expression of quantitative traits. Therefore, recognizing that quantitative traits involve multiple genes and are measurable highlights their complexity and variation, making the provided definition the most accurate.