Transcript GENETICS - St. Bonaventure University

GENETICS
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What is Genetics?
The Study of similarities and differences between
relatives.
What is it that
elephants have
that no other
animal has?
What is Genetics?
The study of similarities and differences between
relatives.
What is it that
elephants
have
that no other
animal has?
Baby Elephants!
Why do we resemble our parents?

Our parents provided most of the information (in the
sex cells) that governs our appearance, our activity,
and our behavior.

They provided most of the GENES.

Genetics is also seen as the study of
Genes or genetic variation.
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Genetics Attempts to Answer These
Questions:
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1. How are Genes Transmitted?
2. What are Genes?
3. How are Genes (the genetic material)
organized to function efficiently?
4. What kind of activities do Genes control?
5. How do Genes control these activities to
produce the differences we see?
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Early ideas about inheritance
Archeological evidence
from 8,000 – 1,000 B.C.
shows horses, camels,
and oxen had been
domesticated and that
various breeds of dogs
had derived from
wolves, through
artificial selection.
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Early ideas about inheritance

Cultivation of many plants,
including wheat, corn and
rice as well as the date palm
began as early as 5,000 B.C.
wheat
corn

The appearance of new
varieties from unconscious
attempts to breed and
cultivate must surely have
led in time to conscious
attempts to propagate
desirable traits and the
elimination of undesirable
traits by the breeders.
corn
Rice
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Early ideas about inheritance

The Assyrians were
sophisticated and
experienced breeders
of domesticated
plants and animals
and had artificially
pollinated date palms
(shown at right) by
800 B.C.
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Simple rule of heredity…

These early practitioners seemed to work
from the simple rule of heredity; like breeds
like; … and sometimes unlike!

Select breeds with the desirable
characteristics and breed them!
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The Greek Influence on ideas of
inheritance

Hippocrates – “Humors”, which could be altered
during an individuals lifetime and therefore diseased
or normal, were drawn from various parts of the body
to the semen and passed on to the offspring. This
“pangenesis” theory even formed the basis of
Darwin’s early ideas of inheritance.

Aristotle – semen produced a “vital heat” that
cooked and shaped the menstrual blood giving it the
capacity to produce offspring with the same “form” as
the parent.
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Later ideas of inheritance
(1600- 1850)
Pre-formationism – sex cells
contain a complete miniature
adult (the homunculus) 
Epigenesis – presumably put
forth by Harvey, held that
body structures were not
present in the sex cells, but
were formed anew.
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Other ideas of inheritance

Pangenesis – the inheritance of acquired
characteristics – put forward again by
Jean Baptiste Lamarck.
[the notion was discredited by August Weissman, who cut tails
off mice for 22 generations and continued to get mice with long
tails]

Blending Inheritance – the belief that
characteristics of parents blended like paint, e.g.,
mix blue and yellow and get green paint.
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Gregor Mendel

Seven years after
Darwin published his
theory, Mendel, an
Austrian monk,
published (in 1866) his
findings on inheritance
in peas. Mendel
discovered the rules
governing “vertical”
gene transmission.
Gregor Mendel
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Mendel’s Discoveries (2 laws)

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Mendel’s 1st Law - The Law of Segregation
(essentially has 4 parts)
1. Alternative versions of “genes” account for
variations in inherited characters.
In a simple case, shown here are 2
versions of a “gene”. Where the flower of
the pea plant is yellow (due to gene y) or
purple (due to gene Y). Many genes
have hundreds of alternatives, and might
be expressed thus: Y1, or Y2, or Y3, or Y4,
orY5, etc.
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Mendel’s 1st law (parts 2 and 3)

2. For each character, an
organism inherits 2 “genes”,
one from each parent.

3. If the 2 “genes” differ,
then one, the dominant
“gene”, is expressed and the
other, the recessive “gene”
has no noticeable effect on
the organism’s appearance.
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Mendel’s 1st law (part 4)

4. The 2 “genes” then
separate again when
the organisms forms
sex cells (gametes),
each sex cell receiving
only 1 of the 2 possible
“genes”.
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Mendel’s Discoveries (the 2nd law)

Law of Independent Assortment.

The most important principle of this law is
that the emergence of one trait (e.g., plant
height) will not effect the emergence of
another (e.g., flower color)
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New Offspring = New gene
combinations

Built into the mechanism for gene
transmission is a means for creating
variability. Reshuffling of genes in the sex
cells of the parents creates new
combinations of genes in the offspring.
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Totally new genes can be created by
Mutation.
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Highlights of some discoveries
following Mendel’s work
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1900 - Mendel’s work was rediscovered.
1902 - Sutton proposed that genes were located on
chromosomes.
1944 - The genetic material was found to be DNA.
1953 - Watson and Crick propose a model for the
structure of DNA that also suggests a means
for its faithful replication.
1966 - How DNA worked to control the activities of
the cell had all been worked out
[ DNA  RNA  protein]
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Highlights of some discoveries
following Mendel’s work (cont.)
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1973 – Recombinant DNA molecules formed.
1977 – Sequencing of DNA achieved.
1983 – PCR technique developed.
1990 – First successful gene therapy.
1995 – The Human Genome Project (HGP)
gets underway.
2003 – HGP essentially completed.
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Vertical Gene Transmission


While most of our genes come from our
parents (vertical transmission) – some may
not have!!!
Some of it is coming in horizontally. It seems
that some of our genetic material is coming
from viruses and other parasites that invade
us.
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Horizontal Gene Transmission
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The Human Genome Project (HGP) has
found that there is a lot of the DNA of our
genes that is identical to that of viruses.
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These parasites have the ability to introduce
some of their genetic material into their host’s
(meaning us) genetic material.
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Horizontal Gene Transmission (HGT)
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These viruses have apparently been doing
this for millions of years.
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These viral elements make up 45% of our
DNA and fully 8% of that comes from
retroviruses. HIV is a retrovirus.
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Horizontal Gene Transmission (HGT)
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What are these viral genetic elements doing
in our DNA? Are they having any effect?
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The answer appears to be that they are
having an effect….the complete answer
remains to be discovered when more
research is done.
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What are Genes?
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Genes consist of a
polynucleotide chain
called DNA (or RNA for
some viruses) that
generally exists as a
double helix.
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What are Genes?

The nitrogen bases,
here represented with
the letters: A, T, G, and
C, signify a code that is
translated into one of
the 20 amino acids that
make up every protein
found in every
organism on earth.
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What are Genes?

Each nitrogen base
always pairs with
another base such that
A always pairs with T
and G with C. There
are 3,200,000,000
base pairs in each
human cell, a string
that would stretch 1
meter (ca. 3 feet) in
length.
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What are Genes?

A gene is a string of nitrogen bases that dictates the
manner by which Proteins are made….nothing
more….nothing less.
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Proteins are made up of strings of amino acids.
They function as enzymes (organic catalysts) and as
structural building blocks of the cell.
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A gene, then, is a recipe for making a protein.
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How much DNA (or genes) do cells
have?
Species
Genes
DNA (bp)
E. coli (bacterium)
Yeast cell
Roundworm
Fruit fly
Rice plant
Gallus gallus (Chicken)
Rat
Homo sapiens (human)
Amoeba proteus (amoeba)
4,400
6,000
19,000
13,600
55,000
23,000
30,000
25,000
?
4,600,000
12,000,000
97,000,000
165,000,000
466,000,000
1,000,000,000
2,750,000,000
3,200,000,000
290,000,000,000
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How much DNA (or genes) do HUMAN
cells need?
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First of all, if we assume 25,000 genes in the human,
and use a figure of 3,000 bp per gene then we need
only 75 million bp for all our genes. We have about
3.2 billion base pairs in our DNA!!
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This means we can account for all our genes with
only 2% of the DNA in our cells.
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The rest is referred to as “Junk” or repetitive DNA.
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How is all this genetic material
organized to function efficiently?
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In diploid organisms
like ourselves, the DNA
is organized into
chromosomes.
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What kinds of activities do genes
control?
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Virtually every type of activity a cell or
organism engages in is controlled by
genes…through the formation of proteins.
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There are 2 major types of proteins:
1. Structural – involved in building and maintaining
subcellular structures.
2. Functional – enzymes.
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How do genes control activities?
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Since proteins control essentially all the activities of
a cell, if the cell knows how to make all the
proteins….it doesn’t need to do anything else.
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Enzymes carry out all the reactions in a cell.
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Structural proteins combine with other proteins,
carbohydrates and lipids by a process known as
“self-assembly” to form all the sub-cellular structures
within the cell.
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We know exactly how the cell does this
DNA in the nucleus of the cell
makes a nearly identical copy
of itself and transports this copy
to the site of protein synthesis in
the cell. Using the genetic code,
the message originally present
in the DNA and transcribed into
the RNA copy is translated into
a protein. This process takes only
seconds to accomplish since it is
aided by enzymes.
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Cells translate the message in the
genetic code to create proteins.
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The 4 bases in the DNA are
a recipe for adding amino
acids one by one to make a
protein, and 61 of the 64
possible ways of arranging
these 4 bases in 3-letter
words proscribes an amino
acid. The remaining 3 order
a STOP to the process….the
protein is done.
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We differ from our parents because the
proteins coded from DNA are different!
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Individuals differ from one another in the
specific sequence of bases in their DNA.
1…TAGGCTGGCATTATATGCGAATTG…
…ATCCGACCGTAATATACGCTTAAC…
2…TAGGCTGGCGTTATATGCGAATTG…
…ATCCGACCGCAATATACGCTTAAC…
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Changes in DNA ultimately result in
changes in the amino acid (message)

…TAGGCTGGCATTATATGCGAATTG…
… THE
CAT
SAW THE RAT …
…..…TAGGCTGGCGTTATATGCGAATTG…

… THE
CAT
ATE
THE RAT …
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The HUMAN GENOME PROJECT
We have just completed sequencing the entire
human genome and there are exactly 3.164
billion base pairs in the human genome.
The best estimate is that there are only 25,000
genes, half of which we don’t yet know the
function.
The rest consists of highly repetitive sequences
(e.g., TTTGGCTTTGGCTTTGGC) repeated
over and over thousands of times.
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The HUMAN GENOME PROJECT
Almost 99.9% of the base pairs are exactly the
same in all people! (This still leaves about 3
million base pairs that differ among any two
individuals) Focus on the similarities…
The genome is full of non-coding or “Junk” or
repetitive DNA – but even this can be useful
for DNA Fingerprinting.
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DNA Fingerprinting
Can help to convict the
guilty and exonerate
the innocent.
In a famous case in
England, a rapist was
caught 3 yrs after the
crime when DNA from
the sperm was matched
with his DNA.
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What can we do with all that we have
learned about genes?
The first organism to have its genetic material
completely sequenced was a bacterial virus
(ΦX174). It has 5,386 base pairs. Using this
information, researchers 2 years ago synthesized a
completely artificial virus from lab chemicals that was
100% identical to the natural ΦX174 virus; and it was
able to behave like the natural virus – infecting a
bacterial cell. We have created life in a test tube…
or at least…..duplicated it!
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What else can we do with what we
have learned about genes?
We can isolate individual genes from any
organism or individual.
We can make millions of copies of that gene in
a matter of hours.
We can combine that gene with others in what
is called a Recombinant DNA molecule and
insert that into most any organism we
choose. This is called Genetic Engineering
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Genetic Engineering
Human insulin produced
in a bacterium using a
gene obtained from humans.
Bacterium full
of insulin
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Gene Therapy
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The technology may eventually be used to
treat a whole range of inherited disorders…
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…for example, why not introduce the gene
for insulin production into insulin-dependent
diabetics rather than having them rely on
frequent insulin injections?
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Gene Therapy (cont.)
SCID (severe combined immunodeficiency
disease) is a fatal condition due to the
absence of an enzyme, adenine deaminase
or ADA.
 Individuals with this disease lack a functional
immune system. They must be kept in a
sterile environment. They were often
referred to as “bubble babies”.
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Gene Therapy (cont.)
The gene for ADA has
been isolated,
combined with a
harmless virus
(Recombinant DNA)
and introduced into
children with this
condition. The photo
on the right shows one
successful application
of this technology.
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Gene Therapy (cont.)
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Of course, every new
technology has its
downside…
Performance-enhancing drug use
has become a big problem in both
professional and amateur
athletics. Periodic testing for
these drugs probably reduces
their use somewhat.
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Gene Therapy (cont.)
What if athletes began to use “gene doping”,
where genes for Human Growth Hormone
(HGH) or Insulin-like Growth factor (IGF-1)
would be introduced into their muscles? It
would be more effective and essentially nondetectable. Olympic officials are definitely
worried about this happening – fearing it has
the potential to ruin athletic competition as
we know it.
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Gene Engineering
A gene for insect resistance
(Bt) has been engineered
into most all of the corn we
consume, rendering it quite
resistant to the European
corn borer.
Many other fruits and
vegetables have been
engineered for drought and
cold resistance and
resistance to plant diseases.
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GENETICS
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The End