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

• 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

Observations in the Galapagos Islands

• Darwin at first thought they were one species with variation

• 13 species with distinct characteristics

• Their beaks show variation in shape and size– Why?

Darwin’s Finches

• 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

Forming the Theory

• 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

On the Origin of Species

Backlash

What Darwin didn’t know…• How do organisms inherit traits? How are

traits passed on from one generation to the next?

DNA

• We looked at evidence for evolution

• Do you remember what the evidence was?

• What do you remember about heredity?

What do you remember?

• Monk who bred pea plants

• He focused on how traits were passed from one generation to the next

• Early studies in genetics

Mendelian Genetics

• Much later, we would realize that the theories of genetics and evolution are closely linked

• Genetics can help explain evolution

Unifying Theories

• 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

Modern Evolutionary Synthesis

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

• Genes code for different traits

• Individuals have different traits because they have different combinations of gene variations

Genetic Variations and Selection

VERY IMPORTANT!

Evolution acts on genes!

• 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

Remember Meiosis?

• Sexual reproduction and crossing over have the same purpose:– Introduce new varieties

of genetic combinations

Genetic Variation

• Mutation events happen in many different ways

• A gene may be lost, switched, or modified• An individual can also gain duplicates of genes

Mutations

Mutations• Remember!• Mutations can be neutral, beneficial

or harmful!

• 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

Mutations and Survival

• 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

Type 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

Types of Mutations:Gene Duplication

• 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

Homologous Genes

• 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

Pseudogenes

• Pg 313 #5, 6• Pg 320 #34, 35, 36, 54

Homework