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Human Genetics and Evolution
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Genetics and Inheritance
Natural Selection
Historical Fact of Evolution
Humans Today and
Agriculture
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
DNA and GENETICS
• Cells divide and pass on
instructions coded in DNA of
chromosomes
• Each chromosome is a huge
DNA molecule with coded
information
• DNA has dual role:
– DNA replicates to pass on
information
– DNA is transcribed to make
proteins that run cell
metabolism
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
DNA and chromosomes
• Long DNA molecules
(millions of base pairs long)
in nucleus are called
chromosomes
• Each chromosome is
organized and packaged or
wrapped up with proteins
giving it a certain shape
• In humans, 23 pairs of
chromosomes
– 1 of each pair from mother
– 1 of each pair from father
• Total view of all 23 pairs is
called karyotype
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Chromosomes
• Each chromosome is a single
DNA molecule wrapped up within
a special group of proteins giving
it a particular shape
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Genes and Genome
• Genome:
– entire DNA of cell (all DNA molecules)
– also includes DNA of mitochondria, chloroplasts in
eukaryotes
– Thought question: Are viruses, phages, transposons part
of genome?
• Gene:
– Region along DNA molecule that codes for 1 protein
– usually 1000's of base pairs long
– E. coli lac operon is first gene whose regulation and
function was understood at molecular level in coding of
DNA
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
DNA is transcribed and translated to
make proteins that run cell metabolism
• DNA is transcribed to mRNA
• mRNA is translated to amino
acid sequence
• Amino acid sequence folds up
into protein
• Proteins catalyze reactions of
cell metabolism
• This process is called “gene
expression”—the information in
one region of the DNA—a
“gene”—is being expressed so
that the cell’s metabolism can
function
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
2 steps of gene expression
1. Transcription – DNA
is read to make a
mRNA in the
nucleus of our cells
2. Translation –
Reading the mRNA
to make a protein in
the cytoplasm
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Overview of transcription and translation
REMEMBER: A particular region of DNA that has the code to make a particular protein is called a “gene.”
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
DNA is also structured to replicate
• DNA is “double helix”—
two complementary
strands wound in a spiral
• Strands separate and
DNA replicates by filling
in other half of each
separated strand
• Famous Watson-Crick
model (Nobel prize)
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
DNA replicates to pass on information
(to daughter cells in mitosis)
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Changes in DNA sequence
• Mutation—change
in DNA sequence.
• Example:
Changes in DNA
allow bacteria to
resist effects of
antibiotics
• Mutation changes
DNA sequence,
which in turn
changes protein
sequence that
codes for a
specific protein in
one of the many
cell metabolic
pathways
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Mutations can spread through a population
• Mutation allows cell to survive in a new
environment--in this case, in the
presence of penicillin. This type of
beneficial mutations can result in more
individual cells that are resistant to
penicillin and can thereby grow colonies
• The offspring or daughter
cells then continue to
spread throughout the
population, especially
where penicillin is
present. This is natural
selection leading to
evolutionary change!! We
have seen it happen...in the
laboratory...in the "wild."
• Fifty years, ago, almost no
bacteria were resistant to
penicillin. Today, some
penicillin resistant cells are
found in virtually all
bacterial populations.
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
How does evolution happen?
• Darwin’s great idea—natural
selection
• Just like “artificial selection” for
agricultural breeds (in fact, is there
any difference—what is “artificial”
about human involvement?)
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Inheritance and Natural Selection
• Some combinations of alleles, produced during meiosis
and fertilization might be more advantageous
• This is what leads to natural selection. Individuals with
more advantageous traits will survive to reproduce and
pass on those traits.
• Darwin realized that slow changes in inherited traits, due
to natural selection produced the great evolutionary
history of life.
• Before his synthesis of all the evidence, no one could
make sense of living systems. Now, “Nothing in Biology
Makes Sense Except in the Light of Evolution”
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--Theodosius Dobzhansky
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
The Classic Example—Sickle Cell Anemia
Washington University Sickle Cell Webpage
Natural
Selection
DNA point
mutation
Cell/Organism
effects
Heredity/Spread
through population
Species/Community
Larry M. Frolich, Ph.D.
interactions
Biology Department, Yavapai College
Evidence for historical fact of evolution
• Fossil record
– Most rocks contain
fossils
– Long-term change in
biological
communities
– Transitions: origin of
mammals, origin of
birds
• Anatomical
similarities
• Shared
embryological
features
• Shared biochemical
and genetic features
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Humans are primates
• Our closest living
relatives are monkeys
and apes
• We share a common
ancestor, most recently
with apes, farther into
deep time with monkeys
and even farther in with
lemurs and tarsurs
• The living species are not
our actual ancestors—we
need the fossil record to
see them
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Fossil record of primates evolutionarily close to humans
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Mediocre to increasingly good human fossil record (see Smithsonian review article)
Not all fossils on direct ancestral line to humans
Larry M. Frolich, Ph.D.
Past shows many different human and human-like species living Biology
at one
time
Department, Yavapai College
Accident of history—one human species today
• Good solid evidence that living
humans form one single
species—Homo sapiens
– Ability to interbreed
– Little anatomical difference among
populations
– Little biochemical difference
among populations
– DNA and protein analysis show
recent single common ancestor
within 1 million years, perhaps
only 200,000 years ago
• But past was different
(evolution is not planned!)
– H. neanderthalis (200,000 years
ago)
– H. floresiensis (12,000 years ago)
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Homo floresiensis (12,000 years ago, Pacific Island)
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Comparison Neanderthal and Modern human skulls
Good evidence that
Neanderthals buried
dead, had religion,
cultural practices,
used tools
Imagine a world where
another sentient,
culturally-driven
primate lived!
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Humans today
• Dominate planet
• Ecologists have often focused on “wild”
ecosystems
• But most landscapes now have some
human elements, usually very strong
effects
• Is this good or bad? And for whom?
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Development of agricultural
systems were evolutionary events
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College