Essential Cell Biology 5th edition

CHAPTER NINE
9
How Genes and
Genomes Evolve
For a given individual, the nucleotide sequence of the genome in every
one of its cells is virtually the same. But compare the DNA of two individuals—even
parent and child—and that is no longer the case: the genomes
of individuals within a species contain slightly different information. And
between members of different species, the deviations are even more
extensive.
Such differences in DNA sequence are responsible for the diversity of
life on Earth, from the subtle variations in hair color, eye color, and skin
color that characterize members of our own species (Figure 9–1) to the
dramatic differences in phenotype that distinguish a fish from a fungus or
a robin from a rose. But if all life emerged from a common ancestor—a
single-celled organism that existed some 3.5 billion years ago—where
did these genetic improvisations come from? How did they arise, why
were they preserved, and how do they contribute to the breathtaking biological
diversity that surrounds us?
Improvements in the methods used to sequence and analyze whole
genomes—from pufferfish to people—are now allowing us to address
some of these questions. In Chapter 10, we describe these revolutionary
technologies, which continue to transform the modern era of genomics.
In this chapter, we present some of the fruits of these technological
innovations. We discuss how genes and genomes have been sculpted
over billions of years to give rise to the spectacular menagerie of lifeforms
that crowd every corner of the planet. We examine the molecular
mechanisms that generate genetic diversity, and we consider how the
information in present-day genomes can be deciphered to yield a historical
record of the evolutionary processes that have shaped these DNA
GENERATING GENETIC
VARIATION
RECONSTRUCTING LIFE’S
FAMILY TREE
MOBILE GENETIC ELEMENTS
AND VIRUSES
EXAMINING THE HUMAN
GENOME