What is used to represent something too big or too small to be observed directly

The finches on the galapagos island were similar in form except for variations of their beaks. darwin observed that these variations were useful for: attracting a mate defending territory building nests gathering food

Which best describes a gene? a. a sister chromatid b. a chromosome c. a tetrad d. a piece of a chromosome

Explain how paleontologists use trilobite fossils as index fossils for various geologic time periods.