Which statement about natural selection is true? group of answer choices it acts directly on genotypes. it is the same as evolution. it can have an evolutionary effect only if phenotypic differences are heritable. changes in allele frequencies can occur only because of natural selection. it always results in reduced genetic variation.

It can have an evolutionary effect only if phenotypic differences are heritable.

Explanation:

Natural selection is one of the several mechanisms for microevolution that change the allele frequencies of a population. The other mechanisms are genetic drift, gene flow, etc. Natural selection favors the best suitable phenotype under the prevailing conditions. It acts on the genetically regulated traits only. The adaptive traits that impart reproductive and survival success to individuals are favored by natural selection. These traits should be genetic and passed to the progeny to give rise to an evolved population.

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.