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Transcript
Part 5
Intro to Genetics:
Mendel and his Peas
Genetics
• Every living organism has traits
that they inherit from their
parents.
• Genetics is the branch of
biology that studies heredity.
Father of Genetics:
• Gregor Mendel was an Austrian
monk born in 1822.
• After studying math and science,
Mendel worked at a monastery
as a high school teacher.
• In addition to teaching classes,
he was responsible for the
school’s vegetable garden.
Mendel
• Mendel knew that pea
plants reproduce sexually,
meaning the plant
contained male parts that
made pollen (plant sperm)
and female parts that made
an ovum (egg.)
• When the pollen and ovum
unite in fertilization a new
plant is produced.
• Mendel was curious about the
different traits that pea plants Mendel
produced.
• Pea plants can be tall or short,
have purple or white flower,
have wrinkled or round peas,
and several other noticeable
characteristics.
• Since peas plants are easy to
grow, Mendel used them make
observations to study
genetics.
• The genetic work that Mendel
did on pea plants would
become the foundation of
modern genetics
Mendel
• Many of the pea plants in the pea
garden were true-breeding
meaning that if they self pollinated they would produce
offspring with the same traits.
• Mendel prevented self-pollination
by cutting out the male part of
the flowers which contained the
pollen. Then he would take pollen
from a specific flower and apply it
to the female part of another pea
plant so he knew which plants
had been pollinated.
Mendel
• Mendel fertilized a true-breeding tall plant with a truebreeding short plant. He called these the P generation for
parent generation. All of the pea plants that were produced
were tall. He called these plants the F1 generation because
the Latin words for son and daughter (filius and filia) starts
with the letter F. He assumed that the tall trait must be
dominant over the short trait.
Mendel
• Mendel took 2 of the F1 tall plants and fertilized them. The
referred to these plants as the F2 generation because they
were the 2nd generation produced, or the grandkids.
• He expected all tall plants in the F2 generation, but ¼ of
the plants produced were short. Although all of the F1
plants were tall, they must
have held the information to
make a short plant.
trait
(phenotype)
alleles
(genotype)
P generation F1 generation
F2 generation
Tall x short
all tall
3 tall plants & 1
short
TT x tt
Tt, Tt, Tt, Tt TT, Tt, Tt, and tt
Mendel
• Scientist now know that each trait is controlled by
the combination of genes we possess.
• For each gene, we have 2 versions known as
alleles. Some genes are dominant and hide the
recessive allele. This explains why there were no
short plants in the F1 generation but they
reappeared in the F2 generation.
Mendel
F1 cross: TT x tt
• An offspring will get one allele from each parent, so the F1 pea plants
received a T from one parent and a t from the other. Together the Tt
will make a tall plant, but the plant is a carrier of the short gene t, so
it can be given to an offspring to make a short plant in the F2
generation.
Genetics Vocabulary
• Allele - different form of the gene. There are 2 different types of
alleles:
(a) Dominant - trait being expressed (capital letter: T = tall)
(b) Recessive - trait being masked by the dominant allele (lower
case letter: t = short)
• Geneotype - what the gene/alleles (“letters”) are. Remember
that one allele comes from mom and the other allele from dad.
• Autosome - chromosome that determines traits but not gender
(in humans, chromosome pairs 1-22)
• Sex Chromosome - determines gender (in humans, 23rd pair; XX
for females and XY for males)
Genetics Vocabulary Continued
• Genotype - what the genes/alleles (“letters”) are. The genetic
makeup. Genotypes may be either:
(a) Homozygous - when an individual has 2 copies of the same
allele (ex: TT or tt)
(b) Heterozygous - when an individual has different alleles (ex:
Tt)
• Carrier - individual who is heterozygous for an inherited disorder
but does not show symptoms. Carriers can pass the allele to
their offspring.
• Phenotype - physical expression. The characteristic that you see
(ex: tall vs. short; green eyes vs. blue eyes)
Punnett Squares
Punnett Squares can be used to predict
the probability of a trait being passed
to an offspring.
• Genotype: the combination of letters that represent the
alleles
• Example: TT, Tt or tt
• Results are recorded as probabilities or ratios (homo
dominant : heterozygous : homo recessive)
• Phenotype: the inherited traits of the offspring that are
visible
• Example: tall or short
• Ratios are reported as (dominant : recessive)
Punnett Squares
• Monohybrid Cross - involves one trait (ex: Tt x tt). For example,
crossing a plant with purple flowers with a plant with white flowers
• Dihybrid Cross - involves two traits (ex: TtRr x ttrr)
Let’s Practice
1. One cat carries heterozygous, long-haired traits
(Ss), and its mate is homozygous for the shorthaired traits (ss). Use a Punnett square to
determine the probability of one of their
offspring having long hair.
P generation: ______ x ______
Genotypic ratio:
Phenotypic ratio:
Let’s Practice
2. One flower is heterozygous red (Rr) and it is
crossed with a homozygous white (rr) plant. Use
a Punnett square to determine the probability of
one of their offspring having a white color.
P generation: ______ x ______
Genotypic ratio:
Phenotypic ratio:
Let’s Practice
3. In a certain species of pine trees, short needles
(S) are dominant to long needles (s). According
to your Punnett square, what is the probability
of an offspring having short needles if the P
generation is true-breeding?
P generation: ______ x ______
Genotypic ratio:
Phenotypic ratio:
Dihybrid (2 factor) Punnett
Squares:
• Punnett squares can also
be used to determine
the likely inheritance of
multiple traits. Mendel
used dihybrid Punnett
squares to discover
independent
assortment; alleles
randomly sort into
gametes independent of
other traits.
Dihybrid (2 factor) Punnett Squares:
• Steps to complete a dihybrid cross:
1. Create all the possible allele combinations that could be
in a gamete
RrYy  _______________
2. Place the created gametes on the top and side of square
and fill in the squares
3. Label and count each phenotype
Dihybrid (2 factor) Punnett
Squares:
• You could do a tri-hybrid cross to determine the probability of 3 traits
at once, but the Punnett square would have 64 boxes. Typically
determining the inheritance of any more than 2 traits at once are
calculated mathematically without the use of Punnett Squares.
Mendel’s Principle’s
• Inherited traits are determined by genes which are
passed from parents to their offspring.
1. Principle of Dominance: There are 2 forms of each
gene, known as alleles. Dominant alleles will be
expressed over recessive alleles.
2. Law of Segregation: Gametes (sex cells) only contain
one gene for each trait. This means that the
offspring will receive one gene from each parent for
any characteristic. Example: when F1 plants were
crossed to produce the F2 generation, each plant
could give either a tall gene or a short gene to the
next generation.
Mendel’s Principle’s Continued
3. Independent Assortment: Each trait is transmitted
separately to the offspring. For example: if a parent
pea plant gives a gene for tallness to an offspring, it
does not give a gene for green pea color. The gene
for color of the pea is inherited independently from
the gene for height.
• Genes that are on different chromosomes are always
independently assorted to the offspring. [Scientist
now know that some alleles do move together if
they are on located close to each other on the same
chromosome].
Beyond Dominant and Recessive:
Mendel’s work explained a great deal
about inherited traits but it did not
explain everything. For many years,
scientist have realized that not
everything we inherit follows Mendel’s
discoveries . Some things are inherited
differently.
• Incomplete Dominant: neither allele is
completely dominant so the
heterozygous individual is a blending of
the 2 traits:
• White flower X Red Flower  Pink Flower
Beyond Dominant and Recessive:
• Codominant: both alleles are dominant, so both are
expressed
• If the white and red flower were codominant they would
produce offspring with both red petals and white petals.
• Cat fur on calico cats and human blood type are common
examples of codominance.
Beyond Dominant and Recessive:
• Multiple alleles: some genes have more than 2 alleles. Each
individual can only have 2 alleles for each gene, but multiple
alleles make more combinations of 2 possible.
• Rabbit fur is on 1 gene, but there are 4 alleles that code for fur
color.
• Polygenic Trait: traits that are based on the interaction of
many different genes. Many human genes, including skin,
eye, and hair color, are polygenetic. Polygenetic inheritance
allows for a greater variety of traits.
Human Blood Type:
• Human blood type is inherited by codominant alleles
and multiple alleles. This lead to confusion for many
years. People didn’t understand how a person with
type A blood and a person with type B blood could
have a baby with type O blood.
• Blood type is determined by the presence of an antigen
on the surface of red blood cells. A cell can have an A
antigen making the person type A, a B antigen makes
the person type B, both antigens on the cell makes the
person type AB, or if neither antigen is present the
person is type O.
Human Blood Type:
• It is important to only get blood transfusions from an
appropriate match, because your immune system will attack
any cells containing antigens that it doesn’t recognize.
• The genotype of blood is written with an I, not an A and B. This
shows that the different alleles are on the same gene.
• Type O blood = universal donor
• Type AB blood = universal recipient
Sex-Linkage
• If a trait is autosomal, it will appear in both
sexes equally . If a trait is sex-linked, it is
usually seen only in males.
• Genes that are carried on the X
chromosome are called Sex-linked genes
because they are inherited with the
chromosome that determines gender.
• Traits determined by sex-linked genes are
called sex-linked traits and can be predicted
with Punnett squares using X and Y.
Sex-Linkage
• Female- (XX) She must
have two recessive alleles
to express the recessive
phenotype.
• Male- (XY) He only needs
one recessive allele to
express the recessive
phenotype.
Colorblindness
X C = Normal X
chromosomes
Xc=X
Chromosome with
colorblind gene
Y = Normal Y
chromosome
http://critiquewall.com/2007/12/1
0/blindness
Possible Combinations:
• XC XC - Woman w/ normal vision
• XC Xc - Woman w/normal vision &
Carrier for colorblindness
• Xc Xc - Colorblind woman
• XC Y - Man w/normal vision
• Xc Y - Colorblind man
*Carrier - Heterozygous for a
recessive trait.
Colorblind mother
Normal Father
C
Y
X
X
c
c
X
C
c
C
c
X X
X X
Results:
c
X Y
c
X Y
Colorblind mother
Normal Father
C
X
Y
X
c
c
X
Results:
C
c
C
c
X X
X X
c
X Y
c
X Y
Female Carriers/ Male colorblind
Try the following problems
on your paper. Be sure to
give the genotypic and
phenotypic ratios.
Carrier mother
Normal Father
Y
X
X
X
Results:
Carrier mother
Colorblind Father
Y
X
X
X
Results:
Colorblind mother
Colorblind Father
Y
X
X
X
Results:
Normal mother
Colorblind Father
Y
X
X
X
Results:
SEX-LINKED DISEASES
1. HEMOPHILIA
2. COLOR BLINDNESS
3. DUCHENE MUSCULAR
DYSTROPHY
4. MALE PATTERN
BALDNESS
Part 6: Genetic Engineering
Making changes in the DNA
How can a sheep that is 12 years old have an identical twin that
is only 4 years old?
How many different dog breeds are featured in a dog show?
How are new varieties of plants and crops produced?
Genetic Engineering
• For hundreds of years humans have been
manipulating the genetic traits of organisms. This
manipulation is called genetic engineering – a
technology in which the DNA of a living cell is
modified
• The oldest form of genetic engineering is selective
breeding, where people only allow animals or plants
with desired characteristics to reproduce. Through
selective breeding, humans have produced many
different dog breeds. Dog breeds which are better
hunters, companions, etc.
Uses of Selective Breeding
• Nearly all domestic
animals – including
horses, cats, dogs
and farm animals &
most crop plants
have been produced
by selective
breeding.
Types of Selective Breeding
1. Hybridization: the selective breeding of 2 dissimilar
individuals, so you can have the good traits of both.
• Example: freeze resistant plants can be crossed with fruit
bearing plants to create fruit plants that can better survive
the winter.
• Example: combine the disease resistance of one plant with
the greater food-producing ability of another to create
desirable characteristics a farmer needs to increase food
production
Types of Selective Breeding
2. Inbreeding: the selective breeding of 2 similar
individuals to continue their desired traits.
• Example: purebred dogs
• Inbreeding will ensure that the characteristics
that make each breed unique will be
preserved. However, inbreeding will also
increases a breed’s susceptibility to diseases
and deformities as a cross between these two
individuals will more likely bring together 2
recessive alleles for a genetic defect
- Example: hip dysplasia in labs and German Sheppards
Hip Dysplasia
Types of Selective Breeding
3. Inducing mutations through the use of radiation or
chemicals.
• Bacteria have been mutated to digest oil - used to help clean
up oil spills.
• Plants have been mutated to produce greater vegetation or to
resist insects, cold and drought.
• In plant breeding, chemicals have been used to prevent
chromosomes from separating during meiosis. As a result,
these chemicals have produced cells that have double or triple
the number of chromosomes. Plants grown from these cells
are called polyploid because they have many sets of
chromosomes.
Types of Selective Breeding
• Polyploid is usually fatal but for some unclear reason,
plants can tolerate the extra set of chromosomes.
Polyploid can produce a new species of plant that is
larger and stronger than their diploid relatives. Many
crops such as bananas and citrus fruit have been
improved this way.
Manipulating DNA
Since DNA was first discovered, scientists have
learned a lot about DNA and now they are working on
ways to change it. We will study a few of the tools
scientist use to study DNA but first…..
Human Genome Project
The Human Genome project first began in 1990 with
scientists in the United States and around the world.
It had two goals:
• Identify and map every gene to its chromosome
• Determine the entire DNA sequence for the human
gneome.
In 2000, all 3.2 billion base pairs of the DNA that makes
up the human genome was identified. One of the
surprising things about the human genome was the
large amount of DNA that does not code for proteins
called introns.
Scientist discovered that human cells contain only
about 30,000-40,000 genes ( that is only double the
number of a fruit fly!)
Gene Therapy
• Information from the human genome is being used to
try to find a cure for genetic disorders by gene
therapy. In gene therapy, an absent or faulty gene is
replaced by a normal gene. Scientists have attempted
gene therapy with the use of viruses because of their
ability to enter a cell’s DNA. First the virus particles
are modified so that they cannot cause disease. Then
a fragment of DNA containing the replacement gene
is spliced onto the viral DNA. The patient is then
infected with the modified virus particles which
should carry the gene into the cells to correct genetic
defects. To date, gene therapy has not been
successful. It still remains as an experimental
procedure for diseases such as cystic fibrosis,
muscular dystrophy, diabetes and hemophilia.
Genetic Research Tools:
DNA Fingerprinting: It is a quick and accurate
procedure of comparing the DNA sequence of any two
organisms. Remember that other than identical
twins, no two individuals have the same genetic
information.
Steps to DNA Fingerprinting:
1. DNA Collection: your DNA is the same in every cell of
the body, so it can be gathered from spit, blood, hair
follicles, blood, semen, skin or any other substance
containing cells.
2. Cutting the DNA: DNA is too long to analyze in one
piece, so it needs to be cut up by restriction enzymes.
There are hundreds of restriction enzymes and each
will cut at a specific place on the DNA sequence.
Steps to DNA Fingerprinting:
3.Separating the DNA Pieces by a Process Called GelElectrophoresis: fragments of cut DNA are placed into
a special gel which is then placed into an
electrophoresis chamber. DNA is a negatively charged
molecule so it moves towards the positive end of the
chamber when electricity is turned on. Since the gel
is thick, the large DNA fragments have a difficult time
moving through the gel.
At the completion of the gel electrophoresis process,
the larger DNA pieces will be near the start and the
smaller DNA fragments will have traveled the farthest.
Each individual will have a unique pattern of the DNA
banding (except identical twins).
Gel Electrophoresis
The resulting DNA fingerprint (bands) looks like the
bar codes used by scanners in stores
Uses of DNA Fingerprinting
1. Identify the genes to diagnose inherited disorders.
2. Develop cures for genetic disorders.
3. Criminal cases – forensics
4. Paternity cases
5. Personal identification – used by the U.S. armed
forces to identify causalities or persons missing in
action. This is better than dog tags or dental records
used in the past.
Copying DNA with PCR
PCR (Polymerase Chain Reaction) is a process where
scientists can copy DNA before testing it. Why? A
detective finds a single hair as the only evidence of left
at the crime scene. Will this hair provide enough DNA
to analyze with DNA fingerprinting? More DNA will be
needed. It must be replicated and then stored.
The DNA is heated to separate the double strand, then
cooled to allowed replication to occur. Every cycle of the
PCR doubles the amount of DNA.
Steps to PCR
1. The double-stranded DNA sample to be copied is
heated which separates the strands.
2. When the DNA cools, short pieces of artificially
made DNA called primers are added.
3. An enzyme called DNA polymerase and free
nucleotides bind to places on the DNA where the
copying can begin. The result is two strands of DNA
that are identical to each other and the original
strand.
4. The heating and replication process is repeated
over and over again. Every 5 minutes the sample of
DNA doubles again to make many copies in a very
short period of time.
Copying DNA with PCR:
Transgenic organisms:
Transgenic Organisms
What do you get when you take a sequence of DNA in
jellyfish and add it to the DNA of a pig?
A transgenic organism!
Transgenic organisms:
Transgenic Organisms
Glowing Pigs!
Transgenic organisms:
Genetic Engineering allows scientists to
transfer DNA from one organisms to
another. When an organism contains genes
(foreign DNA) other than their own, they
are called transgenic.
Transgenic plants: one of the 1st transgenic
organisms was a tobacco plant that had the
gene of a firefly inside. The plant glows in
the dark. Many plants now are changed so
that they contain pest or drought resistant
genes.
Transgenic organisms:
Transgenic animals: some livestock have
been transformed with extra growth
hormones so they grow bigger and faster
ex: beef cattle, poultry
Transgenic bacteria: bacteria can be
transformed to make many different human
chemicals ex: insulin, human growth
hormone, clotting factors
Cloning
• A clone is an organism that is genetically identical to another.
Bacteria naturally clone themselves, but scientists have
developed techniques to clone plants and animals. Dolly the
sheep was the first mammal successfully cloned in Scotland in
1997
• Dolly was created by transferring genetic material from the
nucleus of an adult sheep’s udder cell to an egg whose nucleus
(and therefore, its genetic material) had been removed.
• Dolly, therefore, carried the DNA of only one parent
• Dolly died in 2003, about four years short of a normal’s sheep’s
life span
• One question that still remains about cloning is how the genetic
changes in cells used to obtain the nucleus, might affect the
cloned animal’s health
Cloning
Cloning humans could be possible,
but it has not been done yet. Due
to ethical and religious concerns,
cloning humans is illegal in the
United States and most other
countries in the world.
Stem Cells
Humans are made up of trillions of cells, but we each
start out as one cell, a zygote, or fertilized egg. The
first cells made during development are called stem
cells because they can develop into many types of
cells; nerve, muscle, skin, blood, or bone. When a
stem cell is changed into a specialized cell is called
differentiation. Scientist use stem cells in labs to
create various tissues to try to cure diseases.
Stem Cells
In the beginning, stem cells
came only from embryos or
umbilical chords. Now
scientists can use chemicals to
create stem cells from other
specialized cells by reversing
the differentiation process.