DNA sequences that .a. do not code for proteins are structural, with repeated and translocated sections. b. regulate gene expression. c. transcribe mRNA, tRNA, and rRNA. d. are nonfunctional pseudogenes. e. All of the answer choices are correct.

Which of the following must be true for a fossil organism to be useful as an index fossil? a. the fossil organism must be widespread geographically. b. the fossil organism must be abundant. c. the fossil organism must be limited to a short span of geologic time. d. all of the above.