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Genetics & Heredity
Studying genes and how traits are passed
from parent to offspring.
History
In the pasts, scientists argued about how
genetic information was passed down
and cause traits.
Some scientists believed in “___________”
- that the traits of two parents are mixed.
This doesn’t work when a white flower
and a purple flowered plant have a white
flowered offspring.
Some scientists also believed that
________ were responsible for passing on
traits, rather than DNA, because DNA
molecules are so ________ compared to
proteins.
Experiments that led to our
current understandings
about genetics
____________________ took bacteria that were
pathogenic (cause disease) and killed them with
heat. Then mixed the dead bacteria with
harmless bacteria. The harmless bacteria took up
something from the dead, harmful bacteria.
When they were injected into mice, it killed the
mice. Something was being passed from the
dead bacteria to the living ones to
“____________” them into harmful bacteria.
___________________- radioactively labeled DNA
and proteins in viruses. They allowed the viruses
to infect cells and waited to see whether it was
the DNA or the protein that entered the cells to
infect them. It was the _________!
Experiments that led to our current understandings about
genetics
___________ Identified
that in each DNA
molecule
Adenine=Thymine and
Guanine= Cytosine
(“Chargaff’s rule”).
__________________ took
the first picture of a DNA
molecule using a
technique called x-ray
crystallography
___________________used Rosalind’s picture to
determine the structure
of DNA.
What is DNA?
DNA is a molecule made of _________________.
Each strand is composed of a string of subunits
called __________________. The nucleotides are
bound to each other by covalent bonds.
Each nucleotide has three parts- a sugar (called
_____________), a ___________, and a _________
(either adenine, guanine, cytosine or thymine).
The two strands are wound together into a shape
called a ___________________.
Along the outsides of the helix are repeating
sugars and phospates- the sugar-phospate
__________________.
In the center of the molecule, the bases are
bound together using weak ___________ bonds.
Adenine always bind with thymine and guanine
always binds with cytosine.
What is DNA?
What is DNA?
In a cell, DNA is arranged into structures called
______________________.
A segment of a chromosome (DNA) that codes
for a specific trait is called a ___________.
When a cell gets ready to make a new cell
(through mitosis or meiosis) the cell must copy or
_______________ its DNA so that the new cell has
its own instructions.
DNA also has a “________________” to it. One end
of each strand is called the 3’ (prime) end and
the other end is called the 5’ (prime) end
The ends of a chromosome are _____________.
They are repeated sequences that do not code
for proteins. They protect the genes in the center
of a chromosome.
DNA Organization
DNA is packaged with proteins to form a
matrix called ___________________.
The DNA is coiled around proteins called
___________ like beads on a string.
______________ describes areas in
chromosomes that are loosely opened when
it’s being copied into a protein.
______________________ describes when areas
of the chromosome that are tightly compacted
and not being used.
Some areas of DNA are even able to move to
new location in the chromsome- these are
called _________________ or jumping genes.
How DNA replicates
An enzyme called _________________ comes in
and breaks the hydrogen bonds holding the two
strands of DNA together. This creates a replication
_________ where the DNA opens up.
_________________ binding protein holds the
strands apart while they replicate.
The enzyme ____________ lays down a short primer
of another molecule, RNA, to signal where to
begin. The primer is later replaced by DNA.
The enzyme ___________________ adds new
nucleotides to build the growing strands. It adds
them in a ________________ fashion (A=T and C=G)
How DNA replicates
DNA polymerase is only able to add new
nucleotides in the ___________ direction. This creates
problems that are fixed by copying the two strands
of DNA slightly differently.
One of the strands of DNA is called the ____________
strand because it’s made ________________. The
enzyme DNA polymerase comes in and add new
bases to build a new strand that is complementary
to the template of the leading strand (A binding
with T and G binding with C).
The other strand of DNA is called the _________
strand because it is made _______________. The
enzyme DNA polymerase still copies the DNA, but it
does it in small chunks called ___________ fragments.
These fragments are then joined together into one
continuous strand by the enzyme ___________.
How DNA replicates
How DNA replicates
After DNA polymerase has built
the two new strands, enzymes
called _____________ come in to
check that the copies are
correct. If there is a mistake,
called a ___________, the
enzymes will usually cut out the
mistake and fix it.
When the process of
replication is complete, one of
the old template strands stays
with one of the newly made
strands and the other other
strand goes with the other new
strand. This is called
__________________ replication.
How DNA replicates
When DNA replicates
The process of DNA replication happens before a
cell goes through mitosis or meiosis during a phase of
the cell cycle called “S phase.” The “S” stands for
synthesis of DNA.
G1 and G2 are
phases when the cell
is ______________.
Interphase Is the
term for G1, S, and
G2 phases- when the
cell is preparing to
divide during mitosis
or meiosis.
How does DNA give us our
traits?
DNA gives us our traits by coding for the
______________ that give us our outward
appearances. For example, DNA
determines the color of the protein
pigment made in your eyes and the
amount of melanin pigment made in your
skin that gives you your skin color.
The process by which a protein is made
from DNA is called protein synthesis.
It requires help from another type of
molecule called _________.
RNA
RNA is similar to DNA; they are both
molecules called _____________, but RNA has
some differences:
 RNA is ___________ stranded.
 RNA has no thymine, instead it has a base called
____________ that takes its place.
 RNA isn’t in a double helix shape.
There are three kinds of RNA:
 _________ takes DNA’s message from the nucleus of
the cell to the ribosome.
 _________ transfers amino acids to the ribosome
 _________ is what ribosomes are made of.
Protein Synthesis
The process is broken down into two basic
steps.
The first step is _______________ and it occurs in
the ______________ of the cell. This is when DNA
is copied into RNA by the enzyme RNA
polymerase.
The second step is called __________________
and it occurs at the _______________. The
mRNA goes to the ribsome to give instructions
on how to make the protein and tRNA
molecules carry in amino acids to build the
protein.
Transcription
During transcription the enzyme ________________
attaches to _________________ regions (TATA box)
and begins to build the new mRNA strand in a
complementary fashion. Remember that A=U (no
T’s in RNA) and C=G in a 5’ to 3’ direction. When it
gets to the end of the gene it’s copying there is a
________________ region that usually contains
AAAAAAAA that signals to stop transcription.
Every three “letters” of mRNA is called a _________.
Each codon codes for one amino acid in the
protein that will eventually be made.
Example:
DNA: AAA TTT CCC GGG
mRNA: UUU AAA GGG CCC
mRNA processing
After the mRNA molecule is built during transcription, it
has to be ________________ in several ways before it
leaves the nucleus:
 First, It receives a _________ made of Guanine
nucleotides on one end and a __________ on the
other end. These protect the molecule and control its
transport.
 Next, pieces of mRNA segments are removed. Those
segments that are moved are called _________(they
stay in the nucleus) and the segments that leave and
are attached back together are called _________
(they exit the nucleus). The introns are cut out and
exons glued back togther by molecules called
________ (small nuclear ribonucleoproteins).This
processing allows several proteins to be made from
the same gene.
After the mRNA has been
processed, it moves from
the nucleus of the cell to
the ribsome.
The mRNA moves through
the ribsome and every
three bases/letters- a
codon- tells which amino
acid to add next.
tRNA molecules carry in
the ______________ and
drop them off to build the
protein. The tRNA knows
which amino acid to drop
off because it has a three
letter sequence called an
________________ that
matches in a
complementary fashion
to the codon of mRNA.
Translation
Translation
The ribsome has
three sites where
translation takes
place:
 The A site: where the
tRNA is
________________.
 The P site: where the
_________________
(protein) is built
 The E Site: where the
tRNA ___________ the
ribosome
A summary of protein
synthesis
Codon Table
You can look the mRNA
made from a gene on
a codon table to figure
out what the protein is
that will be built.
Bacterial Genetics
Bacteria are __________________ and don’t
have a nucleus or organelles. They do have
ribosomes.
Bacteria reproduce by a process called
_________________ - it is asexual reproduction.
Bacteria have only _____________ main
chromosome. It is a _________ chromosome,
rather than linear as chromosomes are in
eukaryotes.
Bacteria also have small, extra pieces of
circular DNA called _______________ that they
are able to swap with other bacteria.
How bacteria get new
genes
There are three ways that bacteria
swap DNA:
______________- two bacteria join with a tube
called a pillus that allows them to swap
plasmids.
______________- when a bacteria gets new
DNA from a virus that infects it.
_________________- when a bacteria picks up
a piece of DNA from the environment.
Viruses are ____________
of cells.
Viruses are specific to
specific types of cells
they parasitize. For
example,
_______________ or
phages for short, only
attack bacteria.
Viruses have a
_______________ (either
DNA or RNA)
surrounded by a
protein coat called a
___________. Some
virsuses also have an
_____________ that
helps them to
penetrate hosts cellsit’s made of
phospholipids and
proteins.
Viral Genetics
Viral Reproduction
There are two basic cycles that viruses follow:
 __________ cycle- the virus gets into the host cell and
integrates itself into the host DNA. The host cell makes
copies of the virus and the viruses erupt from the cell,
killing the cell in the process. The new virsuses then go
infect other cells and repeat this process.
 _______________ cycle- the virus incorporates its DNA
into the host DNA but then sits dormant. The dormant
virus is called a provirus. IT remains inactive until some
trigger, usually from the environment, causes the virus
to begin the lytic cycle again.
Viral Reproduction
Retroviruses
Some viruses use _______ to carry their genetic
information instead of DNA. They are called
retroviruses.
They contain an enzyme called _______________
______________ that will copy their RNA into DNA.
This DNA can then be integrated into the host cells
DNA and the lysogenic cycle can proceed.
__________ is an example of a retrovirus.
Gene Regulation
Every cell in your body contains the
______ DNA, but some genes are shut off.
For example, your eyeball cells don’t
need the same proteins as your liver cells.
In humans these genes can be shut off by
_______________ them. There are also
regulatory genes that can promote or
inhibit the transcription of certain genes.
Gene Regulation in Bacteria
Gene regulation has been studied the most in bacteria.
Bacteria have sequences called __________ that control
gene regulation.
An operon contains 4
components:
_______________ geneproduces a _________ protein
that will block RNA
polymerase from making
mRNA.
___________ region- a
sequence of DNA where RNA
polymerase attaches to start
transcription
___________ region- where
the repressor protein can
bind
____________ genes- the
genes that are being
controlled
Heredity Background
A ________ is a segment of DNA that codes for a trait.
An _________ is a version of a gene. For example,
there is an allele for purple flowers (P) and an allele
for white flowers (p) in pea plants.
To talk about alleles we use letters. We usually use
the first letter of the dominant trait to represent the
gene and the lower case version to represent the
recessive gene.
 A ______ is the location of a gene on a
chromosome.
In a diploid organism all cells contain two copies of
every chromosome, one they have inherited from
their mother and one they have inherited from their
father. These are called _____________ chromosomes.
These two chromosomes have genes for traits in the
Heredity Background
The alleles are referred to as being either
dominant or recessive. The dominant gene will
_____________ the effect of the recessive gene.
The genes that an individual has are its
____________. The appearance it has is its
_____________.
There are three possible genotypes:
 _______________ -having one dominant and one
recessive allele (Pp) - the phenotype will be dominant
 ____________________- having two copies of the
dominant gene (PP)- the phenotype will be dominant
 ____________________- having two copies of the same
recessive gene (pp)- the phenotype will be recessive
Mendel & His Pea Plants
Gregor Mendel was the first person to realize that traits
are inherited in a predictable way. He didn’t know
about DNA.
Mendel made what he called “__________________”
pea plants- meaning that they always produced
offspring that looked like themselves (they were
actually ____________________).
He crossed a true breeding purple pea plant with a
true breeding white pea plant and realized that it
always produced all ____________ pea plants.
He repeated this experiment looking at other traitsflower position (axial or terminal), height (tall or short),
pea color (green or yellow), and pea texture (round or
wrinkled) and every time _______% of the offspring
showed only one of the traits.
He called the trait that showed up ___________.
Mendel & His Pea Plants
Mendel then took the experiment a step
farther.
He crossed two of the offspring from his first
cross.
He always saw a ______ ratio of dominant:
recessive. So, for example, he saw 3 purple pea
plants for every 1 white pea plant.
He called the trait that came back the
_____________ trait.
We can now explain the results of Mendels
experiments using a tool called a ____________
___________. His experimental results can also
be replicated in other organisms.
Punnett Squares
A cross looking at only
one trait (flower color) is
called a ______________
cross and requires a box
with four squares.
The mother’s gametes
(eggs) are put on one
side and the father’s
gametes (sperm) on the
other side. Each box
represents a possible
__________________.
Punnett
Squares
A ______________
cross looks at two
traits. For
example, pea
color and pea
shape. It requires
a punnett square
with 16 boxes.
When two
double
heterozygous
individuals are
crossed, it will
always produce
a ____________
ratio.
A Test Cross
A ________________ is a
special type of
monohybrid cross used
when you don’t know
the genotype of an
organism with a
____________
phenotype. For
example if you have a
purple flowered pea
plant it could be PP or
Pp. To figure out which
it is you would cross the
plant with a
homozygous recessive
individual.
Incomplete Dominance
This is a special type
of inheritance where
the dominant allele is
not completely
dominant over the
recessive allele. This
produces a
______________
appearance. For
example, if you cross
a red snapdragon
(RR) with a white snap
dragon (rr) the
heterozygous
offspring (Rr) are pink.
Codominance
In codominance, there is more than one dominant allele. If
a person has both of them they will ____________ them both.
For example, in human red blood cells there are several
genes (multiple alleles) for blood type: A, B, and O. A and B
are codominant.
Epistasis
This occurs when one
gene affects the
_______________ expression
of another gene. IT occurs
in fur in mice. One gene
codes for the presence or
absence of pigmentation.
The other gene
determines the color of
the pigmentation, if it’s
present.
 In Labrador retriever dogs, the dominant gene C
determines if the pigment will be deposited in the
hair. C=pigment c=no pigment. The different colors
of labs are: black (BB or Bb), chocolate (bb) or
yellow (cc) regaredless of the other genes (B, b).
What is the coat color?
 CCBB=
 Ccbb=
 ccBB=
Pleitropy
When a single gene has __________ than
one effect on an organisms phenotype.
For example, the gene for sick cell
anemia causes: an abnormally shaped
red blood cell, poor circulation, damage
to the heart, kidneys, brain, and other
organs, anemia, pneumonia, heart and
kidney failure, bone abnormalities, etc.
Polygenic Inheritance
This is when ________ genes
contribute to a phenotype.
For example, human height
and skin color are
controlled by many genes.
This causes phenotypes that
are not just short or tall, but
rather a continuous
variation.
 The height of a plant is a result of polygenic
inheritance involving 4 genes, each of which
adds 2 cm. to the base height of the plant.
The base height of the plant is 6 cm.
 If a tall plant (AABBCCDD) is crossed with
a base height plant (aabbccdd) what is the
height of the F1 plants?
When Punnett Squares Don’t Work
Punnett square can correctly
predict inheritance when two
genes are on _____________
chromosomes and separate
independently into gametes.
When two genes are on the
same chromosome we say
they are ___________. Linked
genes do not separate
independently into gametesso they are more likely to be
inherited together. If two traits
are linked, the offspring will
look more like the parents,
rather than the way you
would predict using a
punnett square.
Sex Linked Inheritance
Humans and many other animals
have an X and a Y chromsome
that determine their gender
(XX- __________, XY- _________).
All other chromosomes
are called ________________.
When a gene is located on a sex chromosome,
certain genders are more likely to inherit that gene.
We can still predict inheritance using a punnett
square, we just figure in sex.
Red-green color blindness and baldness are both sex
linked traits.
X Inactivation
In females, one of the X chromosomes in every cell in
the body is randomly shut down into a compact
structure called a _________________- it no longer codes
for proteins.
A very visible example of this is in calico cats. Their
yellow and black colors
are caused by a gene
on one x chromsome
(the white color is on
an autosome).
Pedigrees
A pedigree is a family tree that shows the inheritance of a
trait. A square represents a male and a circle represents a
female. A shaded individual has the trait in question. It is
often possible from the pedigree to determine the
genotype of individuals and to determine whether a trait
is dominant or recessive. _______________ traits can skip
generations, ___________ traits show up in every
generation.
Karyotypes
A karyotype is a
picture of all of the
chromosomes in a cell
from an organism. It is made
by adding a chemical during
_______________ that breaks down
the spindle fibers in a cell.
The cell is then squished
and a picture of the
chromosomes is taken. The chromosomes are then lined up
from largest to smallest.
This allows geneticists to see if a person has an extra, missing
or abnormal chromosome.
Mutations
A mutation is a _____________ in DNA. It can be caused by
environmental factors, such as chemicals or sunlight, or can
be caused by an error during replication. There are many
types or mutations:
 A point mutation- impacts only one base (this is the most
common type of mutation)
 An insertion- a new base is inserted
 A deletion- a base is removed
 A duplication- a base is copied
 A translocation- a segment of DNA is moved from one
chromosome to another chromosome
 An inversion- a segment is flipped
 A nonsense mutation- inserts a stop codon that prevents
a protein from being made
 A missense mutation- changes the protein being made
Mutations
 Mutations are usually neutral or have no affect.
There are two reasons for this:
1. Mutations that occur in introns will not be
expressed in the protein being made.
2. Mutations that affect the third letter in a codon
often don’t change the amino acid that gets
added due to redundancy in the genetic code.
This is known as the wobble effect.
 Mutations can also be harmful or even
beneficial if they make a protein work more
efficiently.
 Mutations are an important source of new
genetic variety. This is where new traits come
from.
DNA Technology
Biologist have utilized their knowledge of
genetics, inheritance and DNA to
manipulate it for useful purposes.
Because the DNA in every individual is
different, DNA can be used to identify
individuals or to compare species.
This information can tell us about how
different species have evolved and their
genes have changed over time. It can tell
us if an individual’s DNA was found at a
crime scene. It can also tell us who a
person’s parents are.
Gel Electrophoresis
Gel electrophoresis is a process that allows us to identify
individuals for crime or paternity cases, among other uses.
To create a __________________ using gel electrophoresis
the DNA must first be chopped up into pieces. Enzymes
called _________________ are added to chop up the DNA.
These enzyme cut the DNA at predictable locations, but
the locations vary from person to person. The variation in
sizes of the fragments from each person are called
restriction fragment length polymorphisms or _________.
After the DNA is chopped up it is placed in an agarose
gel which is covered in a buffer. Electricity is then applied.
This causes the ____________________ of DNA to move
farther towards the positive end of the gel (DNA is
_____________ charged).
The DNA is then stained so that the unique bands can be
observed and compared.
Gel
Electrophoresis
PCR
 Polymerase Chain Reaction (PCR) is a
machine that is capable of making
many ___________ of DNA in a short
period of time. This is very useful if only
a tiny amount of DNA is found at a
crime scene. The process is very
similar to DNA replication in a cell.
 First, the strand of DNA to be copied
is placed in a test tube with the
following: primers to signal where to
start copying, nucleotides to be used
to build the new DNA strands, and
Taq polymerase (a DNA polymerase
that is stable at high temperatures).
 The machine then heats up to
separate the DNA strands (instead of
helicase doing this) and the DNA is
copied. The machine cools down
and then heats back up again,
allowing an ______________ amount of
DNA to be made.
Recombinant DNA
Recombinant DNA refers to DNA from two
organisms that has been _____________. Scientists
have inserted animal DNA into other animals,
animal DNA into plants, animal DNA into bacteria
and animal DNA into viruses.
This has allowed us to make genetically modified
foods that possess traits, such
as a longer shelf life or new vitamins.
It has also allowed us to make
bacteria that will produce human
proteins, such as growth hormone
or insulin.
How to make a recombinant bacteria
First the “____________________” is cut out using restriction
enzymes. Then the plasmid from the bacteria is also cut open
using the restriction enzyme. This produces ______________single strand ends of DNA that will bind with each other. The
plamid that’s used also has a gene for ______________________
on it.
The gene of interest and the plasmid are mixed. The enzyme
________ will permanently bind the sticky ends to each other.
Next the bacteria is tricked into taking up the plasmid
(transformation) from the environment. The bacteria will now
express the protein. The bacteria that are recombinant can
be selected for by growing the bacteria on _______ dishes with
antibiotics.
Recall that human DNA has __________, which bacteria don’t
have. Because of this we must use processed mRNA from
humans and then make DNA from it using the enzyme reverse
transcriptase. This copy of the human DNA (lacking the introns)
is called ___________.
How to make a recombinant bacteria
Gene Therapy
Gene therapy is an attempt
to change the DNA in a
human to “correct” it.
Scientists have attempted to
do this by creating a
recombinant virus capable of
changing the DNA in specific
human cells.
The first trials with gene
therapy involved children
with SCID-1 (boy in bubble).
4 of the 9 children cured
developed leukemia.
DNA Sequencing
Machines are capable of automated DNA
sequencing.They are loaded with four
nucleotides (A,T,C, G) that flouresce when they
bind with a complementary base. The DNA being
sequenced is fed through the machine and the
machine reads the glowing bases in order. The
human genome and the genomes of many other
organisms have been sequenced in this way.