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Heredity
Why we are the way we are
Galapagos Islands 1835
 The HMS Beagle arrives from
England to survey the
harbors.
 A young man on board
named Charles Darwin
begins to explore the islands.
 He notices that the there are
different kinds of birds on the
island that look similar, but
are quite different.
 He notices the same thing
about sea tortoises in the is
Why the difference
 The islands are about 500
miles from the mainland of
South America.
 Any animal that just
happened to get there from
the mainland, had a one way
ticket.
 Once on the island the
animals began to find a way
to survive.
 As different animals chose to
survive off of different things
their bodies began to change.
Natural Selection - Giraffes
 Giraffes have long necks
and tall bodies.
 The huge bodies, protect
them from most predators,
and enable them to eat
leaves high in the trees
where there is no
competition from other
animals, but how did they
get this way.
 Darwin theorized that
traits are naturally selected
by how animals live.
 For example the giraffes
that just happened to have
longer neck were more
likely to survive, mate, and
create baby giraffes.
 Those with shorter necks
were less likely to survive,
and so the short neck trait
would die out.
Darwin’s Finches
 The birds on the islands were
found to have subtle
differences.
 Some had developed beaks
for eating nuts, some for
fruits, some had become
good at hunting insects.
 They had most likely all
started from a small group of
a few finches, but over time,
natural selection had caused
changes to their species.
Bird Beaks – Which ones would be
good for different kinds of food?
Survival Advantage
 Certain traits give animals
a survival advantage. For
example, the giraffe usually
has plenty to eat because he
is the only one that can
reach the leaves 20 feet up
in a tree. His height also
gives him the ability to spot
predators early, and his
long legs make him hard to
kill.
Ptarmigan
 From late spring to early
fall the Ptarmigan (a
flightless bird that lives in
far northern forests) has
plumage that is brown and
green.
 In wintertime the
Ptarmigan’s plumage is
snow white.
 Why? How do these two
things help Ptarmigans
survive?
Winter Ptarmigan
Rabbit Feet
Snowshoe hare
Cottontail Rabbit
Environments
 It stands to reason that if
animals adapt to the place
where they live, then certain
plants and animals can only
be found in certain places.
 Southern California has high
mountains that would be
covered in pine trees
anywhere else in the world,
but they burn so often that
trees don’t grow. Instead
grasses and brush cover the
mountains.
Fish out of water
 So what happens when you
take an animal that has
adapted to its environment
out of that place, and put it in
one that is very different?
 The result is (quite literally)
like taking a fish out of water.
 A fish has developed gills that
get oxygen from water, but
those gills can not get oxygen
from the air.
You can take a plant out of the desert…
 A cactus lives in the desert
where it gets almost no
water.
 Wouldn’t a cactus do really
well, and grow super fast if
you put it in a tropical rain
forest?
 The answer is no, too much
water will kill the cactus
because it is designed for
places where there is little
water.
Polar Bears at the Zoo
 At the San Diego Zoo, you
will find polar bears.
 The Polar Bears almost
never leave their water
because the water is kept at
about 33°
 The bears don’t like to get
out of the water because it
is too warm for them, and
they could overheat.
Seals on land
 A seal is one of the most
graceful swimmers in the
ocean
 It can turn on a dime,
accelerate with lightning
speed, and hunt like a lion
does on land.
 Put a seal on the land and
he becomes bear food,
why?
The Human Advantage
 Humans don’t run very fast.
We can’t bite attackers with
poison fangs. We can’t use
strength to get away from
most animals. We have no
fur, no spikes, no claws, no
teeth for fighting.
 So why are we at the top of
the food chain? Why aren’t
we constantly dinner for
some animal?
 Because we have developed a
truly remarkable adaptation,
our minds.
Where do we get these traits
 We get the traits from our
parents.
 In fact all life gets its traits
from the parents.
 Parents pass the genetic
information on to their
offspring.
 Darwin himself noticed that
species are preserved and
seek their own preservation.
That means that all life tries
to survive and make sure that
their kind continues on, even
if the individual must die.
Like Father (or Mother) Like Son
 Every animal passes along
genetic information to
their offspring.
 This information is used (in
a very complicated way) to
build the offspring, but
those offspring are very
similar to their parents.
Similarities
 The difference between
parents and offspring is
very tiny.
 That is why babies usually
look like adults of their
species, or grow to look
like adults of their species.
 The differences are very
small
Similarities
 All Leopards have spots,
the babies eventually get
them.
 Baby Giraffes have long
legs and necks, and get tall
just like their parents.
 Even animals like tadpoles
and caterpillars that start
out nothing like their
parents eventually grow to
resemble them.
Inherited Traits
 Inherited Traits are things that
are passed from parents to
offspring.
 In animals this could be
stripes on a zebra, spots on a
leopard, or other things.
 What gets passed on are all
the things needed to create a
new member of the species.
 There are small details
though that don’t make a big
difference that are passed
down from parents to
children.
Inherited Traits in Humans
 Eye Color
 Hair Color
 Height
 Some diseases
 Direction of hair growth
 None of these will affect
your status of “human,” but
they do give you the unique
details that make you, you.
Environmental Traits
 Sometimes a member of a
species must make changes
that will look like an
inherited trait, but are caused
by the environment in which
they live.
 A good example is a tree that
lives in a place that is very
windy. The tree grows
slanted. Other members of
the same species grow
straight and tall, but that tree
has had to adapt to its
environment.
Environmental Traits
 Here are some
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environmental traits
Sleep Habits
Farmer’s Tan
Hair Styles
Learned Traits
Growing Sideways
Wearing Clothes
Allergies
Learned Traits
 These are environmental
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traits that humans, and
animals have that have been
taught to them.
You Adding Fractions
Your dog eating from a bowl
Your dog whining to be let
outside for a potty break
Your hamster running to the
cage door when you drop in a
hamster treat, yummy.
Behavioral Traits that don’t have to be
learned (instincts).
 Your neighbor’s cat has kittens,
and your parents let you have one.
The kittens stay in the box with
their mother, until you bring
yours home. You then feed it and
raise it.
 One night, when your kitten has
grown up it goes out and brings
back a dead mouse. Its mother
never taught it to hunt.
 Why did it bring the mouse back?
Where did it learn to do that?
 Are there other instincts that
animals and humans have.
Instincts
 You don’t have to teach a
dog to chase cats.
 You don’t have to teach a
baby to cry or suck on a
bottle.
 You don’t have to teach a
seed that is underground
which way to grow.
 These are all instincts that
are passed on just like eye
color.
So how do we get these traits
 Deoxyribonucleic Acid
(DNA) is like a “blueprint” or
recipe to create you (or
anything else)
 DNA is a tiny strand of four
chemicals called nucleotides.
 These chemicals are adenine,
cytosine, guanine, and
thymine.
 From these four chemicals all
life gets its function.
Cool Facts about DNA
 A person typing 60 words per
minute for 8 hours a day
would need 50 years to write
the entire sequence.
 If that sequence was typed in
one straight line it would be
7,000 times taller than the
Empire State Building
 If all the DNA in your body
was taken out, uncoiled, and
put in a straight line, it would
reach to the sun and back
about 600 times.
So what is DNA
 DNA is like a blue print.
 Imagine a rope ladder
twisted. Each rung of the
ladder is a pair of those four
chemicals (picture) on board.
 This ladder twists and is
crumpled up into a ball.
 The sequence (or order) of
the chemicals are like a code
that your cells can decipher
and use as instructions.
DNA commonalities
 All animals have similar
DNA, humans share more
than 99.9% of the exact
same code, but those few
differences are what make
us who we are.
 DNA is contained in a
Chromosome, it is divided
into sections called genes
(or alleles). These genes
give us our unique
characteristics.
Multiple alleles – dominant and recessive
 Sometimes a person has
more than one allele for a
given trait like eye color.
 In this case your body must
choose one or the other.
Luckily our bodies are
programmed to pick.
 There are dominant and
recessive genes. For eye
color Brown is the
dominant color.
 Certain genes are
dominant. This simply
means that the choice is
already made for your
body. It will go with the
dominant trait.
 A recessive trait is one that
you will carry in your
genes, but will not have.
Your children could have it.
(Punnett Squares)
Dominance
 So if you have all dominant
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traits does that mean you are
a dominant person,
absolutely not! It just means
that your body has a way of
making a choice when two
choices are presented.
In fact some dominant traits
are rather scary.
Short vs. Tall
Polydactylia
Fused Digits
Dwarf Limbs
Mutations (not TMNT)
 A mutation happens when your
DNA sequence is altered.
 For some reason your DNA
sequence gets changed.
 Mutations can happen from
injuries on a cellular level
usually caused by ionizing
radiation, UV radiation,
chemical mutagens or viruses.
 Mutations are always recessive,
but if enough people get
mutated genes it is possible to
pass a mutation on to offspring.
Super Human by mutation
 Most mutations do not bring about
an advantage. Most simply screw
everything up.
 For example a very common
mutation can be seen in older
humans.
 As humans go through their lives
they are exposed to UV light from
the sun. This causes a mutation in
hair cells. The mutation garbles the
genetic code of the hair, instead of
changing color the hair simply stops
having color and the correct
texture and you get wirey, gray
hair.
Mutations are important
 Mutations can be beneficial to
a species.
 Lets say a butterfly is bright
orange.
 The genetic code is mutated
and passed on to the
offspring, the babies are
bright orange except one
which is brown, and very
hard for predators to see
(camouflage). Which baby
butterfly has the best chance
of living to be an adult and
creating more butterflies?
Genetic Tests
 Eye Color – Brown is
dominant
 Cross hands – left hand
dominant
 Earlobes – detached is
dominant
 Hair – Brown hair is
dominant