Which of these is a regulatory gene?
a. structure of the lac operon. it contains definite structures labeled from a to e. letter a marks a gen before structural genes.
b. marks a part of the operon that consists of lac z, lac y, and lac a genes.
c. indicates a structure that moves along the operon.
d. marks lac l. this part is located before the others in the sequence.
e. indicates a molecule that can bind to structure a.

B. Marks a part of the operon that contains lac Z, lac Y and lac A genes

Explanation: Regulatory genes are which are involved in the controlling of the expression of other genes. So, whether a gene will be expressed is dependent on the presence or absence of these regulatory genes.

b

is correct hope this   also i learnd this in middle school

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".