Download The Modern Synthesis: Evolution and Genetics

The Modern Synthesis:
Evolution and Genetics
Charles Darwin
- Born in Shrewsbury, England on
February 12, 1809
- Born into a wealthy family as the
5th of 6 children
- Grandfather, Erasmus Darwin, had
proposed that all life came from a
single organism, “the Great First
Cause”
- Darwin was encouraged to become
a doctor, but was fascinated with the
natural world
The Voyage of the Beagle
• December 27, 1831, he joins the HMS Beagle as a naturalist
on a five year voyage
• The ship’s mission was to map the coast of South America for
Britain
• As a naturalist, Darwin was to observe and collect specimens
How did he begin to craft
his theory of evolution?
Observations in South America
• In Argentina, Darwin
uncovered fossils of the
Megatherium and Glyptodon
• These fossils looked like giant
sloths and armadillos
• The fossils were found in the
same geological range as these
modern animals
• Fossils of marine organisms
also found in the Andes
Mountains
Observations in the Galapagos
Islands
• Island chain 1000 km west of Ecuador
• Discovered many new species with many similarities to species
found on South America
• No native amphibians or large land mammals
– why?
Observations in the Galapagos
Islands
• Marine Iguana:
– Closely resembles
iguanas from the
South American
Mainland
– Is the only known
lizard able to dive
and forage in
water
Observations in the Galapagos
Islands
• Giant land tortoises
– At least five unique
species were found on
different islands
Darwin’s Finches
• Darwin at first thought
they were one species
with variation
• 13 species with
distinct characteristics
• Their beaks show
variation in shape and
size
– Why?
Forming the Theory
• After leaving the Beagle in
1836, Darwin spent more than
20 years gathering evidence
on evolution
• He knew that his theories
would be controversial
• By the time he presented his
theory, Darwin was able to
not only explain that
evolution had happened, but
also how it occurred…mostly
On the Origin of Species
• By 1844 Darwin had
prepared an essay on his
theory of Evolution, but did
not publish it
• 1858 - received a letter from
Alfred Russell Wallace, who
had also concluded that
evolution must be true
• This pressure led Darwin to
publish his theory as On the
Origin of Species in 1859
Backlash
What Darwin didn’t know…
• How do organisms inherit traits? How are
traits passed on from one generation to the
next?
DNA
What do you remember?
• We looked at
evidence for
evolution
• Do you remember
what the evidence
was?
• What do you
remember about
heredity?
Mendelian Genetics
• Monk who bred pea
plants
• He focused on how
traits were passed
from one generation
to the next
• Early studies in
genetics
Unifying Theories
• Much later, we would realize that the theories
of genetics and evolution are closely linked
• Genetics can help explain evolution
Modern Evolutionary Synthesis
• Modern Evolutionary Synthesis: the modern
theory of evolution that takes into account all
branches of biology
• This includes genetics
• It also includes the plate tectonic theory we’ve
looked at
Darwin 2.0
• For Darwin, evolution was the changing of
inherited traits in a species over time
• We now consider evolution as changes in the
gene pool of a species over time.
• Gene Pool: the complete set of all gene
variations within a species or population
Genetic Variations and
Selection
• Genes code for
different traits
• Individuals have
different traits
because they have
different
combinations of
gene variations
VERY IMPORTANT!
Evolution acts on genes!
Remember Meiosis?
• At the end of meiosis, a sex cell has only one set
of chromosomes.
• Reproduction leads to variety: new combinations
of genes (both from mother and father)
– Crossover events lead to even more variety: genes get
shuffled around between homologues
Genetic Variation
• Sexual reproduction
and crossing over have
the same purpose:
– Introduce new varieties
of genetic
combinations
Mutations
• Mutation events happen in many different
ways
• A gene may be lost, switched, or modified
• An individual can also gain duplicates of genes
Mutations
• Remember!
• Mutations can be neutral, beneficial
or harmful!
Mutations and Survival
• Mutations can affect an
individuals chances of
survival
• Missing genes is often
harmful
• Having extra copies of
genes might be useful
– Eg: human populations
that eat a lot of starch
have two copies of
genes for starch
proteins, make double
the protein
Type of Mutations:
Gene
Duplication
This is an important type of mutation
•
• A mutation to a gene can often be harmful, even fatal
• But having an extra copy means that if that gene mutates, there is
still another copy to make sure the cell functions properly
• New and novel mutations may now occur
– Eg: rod and cone cells in eyes
Types of Mutations:
Gene Duplication
• Duplication Mutations:
– Often neutral
– Do not immediately
benefit the individual
– Source of new genetic
material with potential to
evolve into new genes
Homologous Genes
• The mammalian forearms suggested a
common ancestor
• These homologous features arise because of
homologous genes
Homologous Genes
• Homologous genes share a common ancestor,
but have mutated over time
• The more closely related two species are, the
more similar their homologous genes will be
Pseudogenes
• Pseudogene: A vestigial
gene that has undergone
mutations and no longer
serves a useful purpose
• Eg: Dolphins have 1000
genes for olfactory
(smell) receptors, but
only use 200 of them
– Why?
Pseudogenes
• Dolphins have 1000
genes for olfactory
(smell) receptors,
but only use 200 of
them
• Smell receptors
detect airborne
chemicals, so are of
no use to dolphins
Homework
• Pg 313 #5, 6
• Pg 320 #34, 35, 36, 54