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DNA, Heredity & Adaptations
Ch’s 4, 5 & 6(a little)
DNA
 A chemical that contains
information that an
organism needs to grow
and function
 Makes up an code
alphabet that consists of 4
“letters”
 With these 4 letters, all life
is “spelled out”
Watson & Crick
 1952, Rosalind Franklin
discovered that DNA is in
two chains
 From Franklin’s research
and the research of others,
James Watson and Francis
Crick (1953) made a model
of DNA
 They ended up being correct
and won the Nobel Prize
DNA Structure
 The structure of DNA is
similar to a twisted ladder
 The sides of the ladder are
made up of sugarphosphate molecules
 The rungs of the ladder are
made up of nitrogen bases
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There 4 bases: Adenine (A),
Guanine (G), Cytosine (C)
and Thymine (T) (our 4-letter
code alphabet)
A always bonds with T, C
always bonds with G
Genes
 Genes are sections
of DNA on a
chromosome
 Genes contain the
instructions for
making specific
proteins

Humans have about
20,000 to 25,000
genes
Protein Production
 RNA (ribonucleic acid)
 RNA is single-stranded and instead
of Thymine, there is Uracil as a
nitrogen base
 Messenger RNA (mRNA) carries
the code that directs the order in
which the amino acids bond
from the nucleus to the ribosome

“Reads” a specific gene for that
protein and makes a copy
 Ribosomal RNA (rRNA) makes
up ribosomes, where proteins
are built
 Transfer RNA (tRNA) brings
amino acids to the ribosomes to
build the protien
Review Questions
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What are the four nitrogen bases that make up the
“genetic alphabet”?
How are the codes for proteins carried from the
nucleus to the ribosomes?
A single strand of DNA has the bases AGTAAC.
Using letters, describe the matching DNA strand
from this pattern.
How is tRNA used when cells build proteins?
You begin as one cell. Compare the DNA in one of
your brain cells to the DNA in one of your heart
cells.
What type of nucleic acid carries the codes for
making proteins from the nucleus to the ribosome?
Acquired Traits
 Acquired traits are
traits that result
from things that
happen to you in
your life
 Ex:
learning,
physical
accidents, etc.
 Once thought to
be heritable
Heredity
 Heredity is the passing of
traits from parent to
offspring
 Genes on chromosomes
control the traits that show
up in an organism

Ex: gene for ear lobes
 The different forms of a
trait that a gene may have
are called alleles.

Ex: 2 alleles for ear lobes:
attached and unattached
Heredity
 During meiosis, a pair of
chromosomes separates
and the alleles move into
separate cells
 Each chromosome now
contains one gene for
each trait

Either the trait from the
organism’s mother or the
trait from the father
 So each gamete
(reproductive cell) ends
up with one allele for
every gene
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How many alleles for each
gene do the rest of your
cells have?
Why does this need to
happen?
Gregor Mendel
 Gregor Mendel is referred to as
the father of modern genetics
 Genetics is the study of how
traits are inherited
 Mendel was an Austrian monk
who studied math and science

Was also a gardener
 Mendel was the first to use the
mathematics of probability to
explain heredity and to trace
one trait for several generations

He mainly looked at pea plants
Mendel’s Experiments
 When he would cross two plants
with different characteristics, the
offspring would look like one of
the parents
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He called these new plants hybrids
A hybrid is an organism that
receives different genetic
information for a trait from each
parent
 In one experiment, he found that
if he bred purebred tall plants
with purebred short plants, all of
the offspring would be tall
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He called the tall trait dominant –
because it dominated, or covered
up the short form
He called the short trait recessive –
because it seemed to disappear
Another Cross
 Mendel crossed these
new hybrid plants (he
called them the F1
generation)
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What do you think the results
were?
 He found that, on
average, 3 of the next
generation were tall, and
one was short
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So the recessive trait (we call it
an allele) did not disappear, it
was just covered up
 He looked at many traits
and found similar results
Probability
 Probability is a branch of mathematics that helps you
predict the chance that something will happen
 Probability = outcome/possible outcomes

Ex: if you flip a coin, what is the probability that you will get
heads?
 Probability = 1 (it can only land on one side & get one
outcome) / 2 (there are two possibilities on a coin)
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So, the probability of heads is ½ or 50%
 Also, the more trials you perform, the closer you will
get to the expected probability

Let’s toss some coins.
Punnett Squares
 A Punnett square can
help you predict what an
offspring will look like
 Dominant alleles are
represented by uppercase letters
 Recessive alleles are
represented by lowercase letters
 Ex: “A” is tall, “a” is short
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What is the probability of
tall offspring?
What is the probability of
short offspring?
 Let’s practice a couple on
the board
Allele from
parent 1
Other allele
from parent
1
A
a
AA
Aa
Aa
aa
Allele from
parent 2
A
Other allele
from parent
2
a
Genotype and Phenotype
 Genotype is the genetic makeup of an
organism
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Ex: Aa, aa, AA
 An organism with a homozygous genotype
has two alleles for one trait that are the same
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Ex: aa, AA
 An organism with a heterozygous genotype
has two alleles for one trait that are different
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Ex: Aa
 Phenotype is the way an organism looks and
behaves as a result of its genotype
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Ex: tall or short
Review Questions
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Alleles are described as being dominant or recessive. What is
the difference between a dominant and a recessive allele?
How are dominant and recessive alleles represented in a
Punnett square?
Explain the difference between genotype and phenotype. Give
examples.
Gregor Mendel, an Austrian monk who lived in the 1800s, is
known as the father of genetics. Explain why Mendel has been
given this title.
If an organism expresses a recessive phenotype, can you tell
the genotype? Explain.
If an organism expresses a dominant phenotype, can you tell
the genotype? Explain.
What is the probability of rolling a 5 on a standard die?
Hairline shape is an inherited trait in humans. The widow’s peak
allele is dominant and the straight hairline is recessive. Predict
how both parents with widow’s peaks could have a child without
a widow’s peak.
Genetics Since Mendel
 Mendel got almost
everything right

He got stuff right he
didn’t even know the
specifics of
 He just didn’t have
any knowledge of
DNA, genes,
meiosis, etc
Incomplete Dominance
 Neither allele for a trait is
dominant
 The phenotype of a
heterozygous individual is
intermediate between the
two homozygous parents
 Ex: Snap Dragon
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Red flowered (RR) x White
Flowered (R’R’)
What will the F1 generation
be?
Multiple Alleles
 A gene that has more than two possible alleles is
said to have multiple alleles
 Traits that are controlled by multiple alleles produce
more than three phenotypes
 Ex: Blood Type
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There are three alleles for blood type
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IA, IB, and i
IAIA or IAi – blood type A
IBIB or IBi – blood type B
IAIB – blood type AB (also an example of something called
codominance)
ii – blood type O
Polygenic Inheritance
 A group of gene pairs acts
together to produce a trait,
which creates more
variety in phenotypes
 Many human traits are
controlled by polygenic
inheritance
 Ex: Skin Color
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It is estimated that three to
six gene pairs control your
skin color
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This provides for a greater
variety of skin tones
Even more control your hair
and eye color
Impact of the Environment
 You only get “potential” from genes
 Your environment plays a role in how some of your
genes are expressed or whether they are
expressed at all
 Ex: the reason male birds are more colorful than
female birds is due to the different chemicals
present in the different genders (also why males go
bald in humans more often than females)
 Ex: you may inherit a greater chance of getting
diabetes, but if you take better care of yourself, you
are less likely to get diabetes
Mutations
 A mutation is any
permanent change in the
DNA sequence of a cell’s
gene or chromosome
 Mutations are caused by
outside factors like X-rays,
sunlight, and some
chemicals
 A change in a gene or
chromosome can change
the traits of an organism
Mutations
 A mutation can be
harmful, beneficial, or
have no effect
 Chromosome
disorders are caused
by more or fewer
chromosomes than
normal
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Ex: Down Syndrome
is caused by an extra
copy of chromosome
21
Recessive Genetic Disorders
 Both parents need to have
had a recessive allele for the
disorder to be passed on to a
child
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The parents usually do not have
the disorder
The parents are heterozygous
 Ex: Cystic Fibrosis
 Most common genetic disorder
leading to death among
Caucasian Americans
 A thin fluid is produced that
lubricates the lungs and
digestive tract
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In Cystic Fibrosis, a mucus
builds up and makes breathing
and digesting difficult
Sex Determination
 Organisms that have two sexes will
have a chromosome that determines
gender
 In humans, it’s the 23rd chromosome
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Females are XX
Males are XY
X
 All eggs from females give one X to
offspring
 Sperm can contain either an X or a
Y
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Males determine gender
 Sometimes, a gamete will get more
than one allele (extra X or Y)
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A number of chromosomal disorders can
occurs
 So what is the probability that a child
will be a male? A female?
Y
X
XX XY
X
XX XY
Sex-Linked Traits
 An allele inherited on
either the X or the Y
chromosome is said to
be sex-linked
 X-linked recessive
traits much more
common in males
 Why?
 Color Blindness
 Caused by a
recessive allele on
the X chromosome
 Much more
common in males
Sex-Influenced Traits
 Some traits are expressed
differently in males and
females
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Why do you think that is?
 Males and females produce
different hormones that
influence gene expression
 Baldness is an example
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Much more common in males
because of the male
hormones (or lack of female
hormones)
Pedigrees
 A pedigree is a virtual tool for tracing a single trait through
generations of a family
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I.e. – sickle cell anemia, blue eyes, etc.
�
Females are circles O
 Males are squares
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 A filled in circle or square means the person has the trait being
traced
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A circle that is not filled in means the person doesn’t have that
trait O
 A circle or square that is half filled in means the person is a
carrier for the trait
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This means they are heterozygous for the recessive trait and it is
not expressed in them, but can still be passed on
 A circle and square connected horizontally means the two
individuals had children
o�
 From that couple, a vertical is drawn downward
and the offspring are written in
Pedigree Example
Uses of Pedigrees
 For a geneticist, it is useful to
understand who has had a trait to
discover it’s pattern of inheritance
 Recessive?
Dominant? Sex-linked?....
 This is why many geneticists come to
Utah
 We
have done lots of good geneology
Section Review
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Compare inheritance by multiple alleles and polygenic
inheritance.
Explain why a trait inherited by incomplete dominance, such
as the color of Appaloosa horses, is not a blend of two alleled.
Describe two genetic disorders and discuss how they are
inherited.
Draw a Punnett square on the board explaining why males
are affected more than females by sex-linked inheritance.
Calico male cats are rare. Explain how such a cat can exist.
A man with blood type B marries a woman with blood type A.
Their first child has blood type O. What other blood types are
possible for their future children.
What is the difference between a sex-linked trait and a sexinfluenced trait.
Draw a pedigree on the board for one trait in your immediate
family.
Genetic Engineering
 Changing the
arrangement of DNA
that makes up a gene
 Recombinant DNA
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Bacteria are wonderful at
reproducing
A useful segment of
human DNA is inserted
into a bacteria (the U of
U uses E. coli )
The bacteria produces
many copies of that gene
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I.e. – an insulin gene for
diabetic patients
Gene Therapy
 A normal allele is placed
into a virus, which delivers
the normal allele when it
infects its target cell
 Hopefully, the normal allele
replaces the infected one
(doesn’t always work)
 Has been used to control
cystic fibrosis
Genetically Engineered Plants
 For a long time, people have
been selectively breeding
plants to get the best crops
 Now, geneticists can insert
genes into plants that produce
desired traits
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A gene for tomatoes that allows
growers to pick them when they
are green and transport them so
they are in the store ripe and red
Review Questions
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Give examples of areas in which advances
in genetics are important.
Compare and contrast the technologies
using recombinant DNA and gene therapy.
What are some benefits of genetically
engineered crops?
How does selective breeding differ from
genetic engineering?
Why might some people be opposed to
genetically engineered plants?
Species
 A species is a group of
organisms that share
similar characteristics
and can reproduce
among themselves to
produce fertile offspring
 Characteristics of a
species are inherited
from parent to offspring
 Any change in these
characteristics over
time is called evolution
Acquired Traits
 Jean Baptiste de Lamarck (1809) proposed
that characteristics, or traits, developed
during a parent organism’s life are passed on
to its offspring
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ex: If you work hard and become smart (even though you
were born stupid), your kids will inherit “smartness”
 Is this true?
Natural Selection
 Charles Darwin (1831
through 1859) proposed
that organisms with traits
best suited to their
environment are more
likely to survive and
reproduce
 known
as natural selection
 the next generation will be
more like the “fittest”
parents
Variation
 A variation is an
inherited trait that
makes an individual
different from other
members of its
species
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result from permanent
changes, or mutations, in
organisms genes
 Examples:
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shape of human
hairlines, coat color of
squirrels, seed types in
Adaptation
 Some variations are
more helpful than
others (ex: bad eyesight)
 An adaptation is any
variation that makes
an organism better
suited to its
environment
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ex: camouflage, speed,
higher order thinking (only
occurs in some humans)
Review Questions
 Compare Lamarck’s ideas with natural
selection.
 Why is variation a good thing for a
population over the long run?
 What is a species?
 What adaptations would be helpful for
an animal species that was moved to
the arctic?