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Family connections:
genes and heredity
From yesterday:
What is evolution?
From yesterday:
What is evolution?
The process of genetic change in
populations of organisms over time
What is necessary for evolution to occur:
Three things:
1. Organisms
multiply in number
(“reproduce”)
2. Children tend to
resemble their
parents
3. Not everybody is
the same
Mechanism by which evolution works:
Natural selection
Mechanism by which evolution works:
Natural selection
• Variation between individuals: some are more
likely to survive than others.
• Some variation is heritable, since children
tend to resemble their parents
• Next generation resembles those who did
best in previous generation
• Given time, lots of small changes add up to
make large changes
What is evolutionary theory good for?
Evolution by natural
selection also explains why:
• Organisms become good at what they
do: “adapted” to their environment &
lifestyle
• In many cases historical contingencies
prevent “optimal” adaptation: “bad
design”
• Organisms have changed over time, as
evidenced by fossils
Thus, fossils are another piece of evidence for evolution
Fossils show transitional forms
For any major
changes in animal
form, we have
fossils that show
the transitions
“Archaeopteryx”
What is evolution?
Fossils show transitional forms
For any major
changes in animal
form, we have
fossils that show
the transitions
“Tiktaalik”
What is evolutionary theory good for?
Evolution by natural
selection also explains why:
• Organisms become good at what they
do: “adapted” to their environment &
lifestyle
• In many cases historical contingencies
prevent “optimal” adaptation: “bad
design”
• Organisms have changed over time, as
evidenced by fossils
Other evidence for evolution
Animal “family trees”
•
•
•
Some classification
works better than
others
The ones that work all
give the same result!
I.e. the number of
legs, the type of
skeleton, the genetic
similarity, all give the
same consistent
“family tree”
Other evidence for evolution
Biogeography
•
•
Every species of plant or animal originates
somewhere. It then may spread, but not if there is
an ocean in between!
How organisms have spread at different times
agrees with what we know about continental drift.
Americas:
• Tomato plant
• Teosinte/Corn
• Potato plant
• Turkey
• Saguaro (almost all cacti)
Eurasia:
• Starling
• Elephant
• Honey bee
• Euphorbia plants
Summary: what evolution is
Variation, Natural selection, and Inheritance
leads to change in a population over generations
•
•
•
•
A logical consequence of what we know about
heredity & survival
An explanation for the appearance of design
in living things (adaptation)
An explanation for many other observations
that would otherwise seem random
coincidences
The intellectual framework for all of biology &
medicine
Joanna Masel: What evolution is and what it isn’t
Heredity & genes
Evolution requires
inheritance of traits. We
know today that traits are
inherited via genes.
What is a gene, and
where are the genes in the
body?
Heredity & genes
Animals and
plants are
built of
thousands of
cells
(~50 trillion in
a human)
- and each one
contains your whole
genetic material!
Heredity & genes
What else is in a cell?
• Membrane
• Genetic material
• Machinery
Heredity & genes
Important molecules in the cell
• Proteins: enzymes
(machines), actin
filaments (skeleton,
transport)
• Lipids (build
membranes)
• DNA
(information/bluepri
nt to build proteins)
Heredity & genes
How DNA works
Enzyme
copying
DNA
chromosome
DNA
double
helix
Heredity & genes
Genes
• Each cell contains a complete copy of
an organisms genome on a long
strand of DNA
• A “gene” is a section of DNA that gets
translated into a protein
• Proteins make up machines, skeleton,
and color of cells  and therefore
determine form and function
Heredity & genes
Genes
• Humans probably have about 30 000
genes – other animals can have fewer
or more
• Similarity between parents and
offspring – “heritability” – is a result of
genes: each child gets a copy of some
of the mother’s and some of the
father’s genes.
Heredity & genes
Gregor Mendel
• A monk who grew
peas
• Discovered that
inheritance is based
on discrete units
(which were later
called “genes”)
Heredity & genes
Two genes for every trait
• One from mother, one from father
• Some are dominant, others recessive
RR WW
RW RW
Heredity & genes
Two genes for every trait
• One from mother, one from father
• Some are dominant, others recessive
• In humans, blue eyes are a recessive
trait, brown eyes are a dominant trait
If my dad has blue
eyes, what is my eye
color? (What is my
brother’s eye color?)
Genes and behavior
Genes and behavior
How do genes influence not
only eye color etc. but also
behavior?
Heredity & behavior
Neurons (=nerve cells)
• Transmit and process information
• Connect to sense organs and muscles
• Brain is an aggregation of neurons
Heredity & behavior
How is the network created?
• During
development,
neurons grow
along certain paths
• Experience
influences the
connections
neurons make
Heredity & behavior
Heritability of behavior
Behavior can be heritable,
• because the formation of the brain and
specific circuits, even the potential to learn,
all require information before learning:
genetic information.
• Any variation in that genetic information is
heritable.
Genes and behavior
Very complicated behaviors can
be determined by genes (and thus
be heritable and evolve)
There is plenty of evidence for this,
even though we don’t always
understand exactly which genes
influence which neurons, and in which
way.
Genes and behavior
Exp 1: solitary animals – cannot
learn from parents or conspecifics
Fiddler crabs: ‘wave’ to attract females, build
burrows in mud to hide at high tide
Genes and behavior
Exp 2: computers – can be
hardwired or programmed to do
complex things without learning
Genes and behavior
Exp 3: human infants – can do
many things
Infants know that two piles of sand poured in a
bucket can be made into any number of sand
piles, but two dolls in a bucket are still two dolls
afterwards
Genes and behavior
Exp 3: human infants – can do
many things
Infants know that two piles of sand poured in a
bucket can be made into any number of sand
piles, but two dolls in a bucket are still two dolls
afterwards
Genes and behavior
Exp 4: breeding studies – if animals
can be bred to do something, it must
be heritable
Swallows were bred to fly south or west; honey bees can
be bred to hoard more or less pollen; dogs were bred to
retrieve or point
Genes and behavior
ALL
competitors
at high-level
sheepherding dog
trials are
Border
Collies – not
other breeds
of dog
Genes and behavior
And why not
cats??
You cannot
teach a cat to
herd sheep,
because it is
genetically
different from
a Border
Collie
Heredity & behavior
Heredity & behavior
Evidence that behavior is
heritable
Many kinds of evidence!
• Artificial selection / purebred strains /
twin studies
• Specific genes identified / heritable
malfunction / mutants
• Differences between species if raised in
lab under same conditions
Heritability vs. aquired traits
However, many traits are not
heritable!
Why? Because
• Developmental effects
• Plasticity
• Learning
can cause differences between
individuals.
Heritability vs. aquired traits
However, many traits are not
heritable!
Why? Because
• Developmental effects
• Plasticity
• Learning
can cause differences between
individuals. NO evolution of these
differences!
Heredity & genes
Genes
• Each cell contains a complete copy of
an organisms genome on a long
strand of DNA
• A “gene” is a section of DNA that gets
translated into a protein
• Proteins make up machines, skeleton,
and color of cells  and therefore
determine form and function
Summary: what evolution is
Variation, Natural selection, and Inheritance
leads to change in a population over generations
•
•
•
•
A logical consequence of what we know about
heredity & survival
An explanation for the appearance of design
in living things (adaptation)
An explanation for many other observations
that would otherwise seem random
coincidences
The intellectual framework for all of biology &
medicine
Joanna Masel: What evolution is and what it isn’t