17.3 Molecular Clocks Study Guide

Flashcards based on the Chapter 17 Section 17.3 notes regarding molecular clocks, mitochondrial DNA, and ribosomal RNA.

What are molecular clocks?

Models that use mutation rates to measure evolutionary time.

How do species become more different at the molecular level after they diverge from a common ancestor?

The more time that has passed since two species diverged, the more mutations build up in each lineage, making the species more molecularly distinct.

How do scientists estimate mutation rates for use in developing a molecular clock?

Scientists must link molecular data with real time, often using geologic events that separated species or the first appearance of species in the fossil record.

What is Mitochondrial DNA ($mtDNA$)?

DNA found in the mitochondria, which are the energy factories of the cell.

Why is $mtDNA$ a good molecular clock for closely related species?

Its mutation rate is relatively high, approximately $10$ times faster than that of nuclear DNA.

How is $mtDNA$ inherited in many species?

It is always inherited from the mother and is passed down unshuffled to offspring.

What is ribosomal RNA ($rRNA$)?

RNA found in ribosomes, which are the organelles that manufacture proteins in cells.

Why is $rRNA$ useful for studying distantly related species, such as those in different kingdoms or phyla?

It contains conservative regions and its mutation rate is relatively low, making mutations that build up over long periods clear and easy to compare.

What two steps are required for scientists to figure out mutation rates?

Counting the number of genetic differences between species and determining how long ago the species diverged from a common ancestor.

What type of molecule serves as the best molecular clock for species belonging to different phyla?

Ribosomal RNA ($rRNA$), because it accumulates mutations at a slow rate.