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Gregor Mendel
Genetics =the branch
of biology that deals
with heredity.
A great deal of what we
know about genetics
began with the work of
a monk named Gregor
Mendel, who
experimented with
sweet pea plants in the
2 1800s.
Mendel’s Work
• Mendel studied the patterns of
inheritance in pea plants.
• He chose seven traits to follow.
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• Mendel needed to
make sure he had
plants that always
gave the same
offspring-called true
breeding.
• He “self-pollinated”
plants until he got
seeds that always
gave the same
offspring.
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 He took a purple
flower plant and
crossed it with a
white flower plant.
 He called these the
parent generation
(P1 generation)
 What do you think
the offspring (the
F1 generation)
looked like?
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Pollen
X
F1
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POLLEN
F2
Mendel concluded:
1. Something is being passed from
parent to offspring.
2. Sometimes you can see “it” and
sometimes you can’t.
3. If you can see “it”- “it” is
dominant.
4. If “it’s” there and you can’t
see “it”- it’s recessive.
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1. Dominant alleles are shown using a capital
letter (R)
2. Recessive alleles are shown using a lower
case letter (r)
Examples: R=red r=pink
RR - ?
Rr - ?
rr- ?
Each version is called an allele.
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Alleles are located on genes on chromosomes.
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Law of Dominance
States that the dominant allele
will prevent the recessive allele
from being expressed. The
recessive allele will only appear
when it is paired with another
recessive allele in the offspring.
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We have two
copies of all
of our
chromosomes
Why?
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BOY OR GIRL?
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What is a gene?
• A segment on the chromosome that
codes for a protein.
• People have two copies of each
gene, one copy inherited from the
mother and the other copy inherited
from the father.
• There are many versions of each
gene-alleles
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•
If the 2 alleles are
different, the condition
is called heterozygous.
The term “hybrid” is
sometimes used to
refer to heterozygous.
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If the two alleles in
the pair are
identical, then the
condition called
homozygous.
Genotype: the
genes or alleles
(RR, Rr, rr)
Phenotype: an
organisms
physical
appearance
(Red, White)
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How did you
end up with
the traits and
genes that
you got?
During
meiosis, each
egg or sperm
only gets one
copy of each
chromosome.
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Law of Segregation
(separation) states that
gene pairs separate when
gametes (sex cells) are
formed, so each gamete
has only one allele of
each gene pair.
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A a
b B
Aa
Aa
bB
bB
A
a
A
a
b
B
b
B
Law of
Independent
Assortment
states that
different pairs
of genes
separate
independently of
each other
when gametes
are formed.
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REVIEW
1. A trait is a characteristic an individual
receives from its parents.
2. Genes carry the instructions responsible for
the expression of traits.
3. A pair of inherited genes controls a trait.
4. One member of the pair comes from each
parent.
5. Alternative versions of genes are known as
alleles.
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REVIEW
Mendel’s Principles of Inheritance
•
Inherited traits are transmitted by genes which
occur in alternate forms called alleles
1. Principle of Dominance - when 2 forms of the
same gene are present the dominant allele is
expressed
2. Principle of Segregation - in meiosis two alleles
separate so that each gamete receives only one
form of the gene
3. Principle of Independent Assortment - each trait
is inherited independent of other traits (chance)
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Punnett Squares
• Used to determine the probability of
a combination of alleles
• Example: If a heterozygous black
rabbit is crossed with a heterozygous
black rabbit, what are the chances
the offspring will be black?
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B=Black
b= Brown
Genotypes?
Phenotypes?
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Example EOCT Question:
Earlobe shape is a human trait. Some people have
free earlobes while others have attached
earlobes. Two parents with free earlobes have
four children. Three children have free earlobes
and one child has attached earlobes. If these
parents have another child, what is the
probability that the child will have attached
earlobes?
A 25%
B 50%
C 75%
D 100%
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Example EOCT question:
In humans, a widow’s peak is dominant over
a continuous hairline. Mary’s father has a
widow’s peak, but Mary and her mother
have a continuous hairline. What is the
genotype of Mary’s father?
A HH
B Hh
C hh
D cannot be determined
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Incomplete Dominance
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Codominance
• a cross between organisms with
two different phenotypes
produces offspring with a third
phenotype in which both of the
parental traits appear together.
• Ex: Yellow and Orange = yellow
with orange spots
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Codominance
• Both phenotypes
are expressed at
the same time.
• Example: Blood
Types
Genotype
IOIO
Phenotype
Type O
IAIO
IAIA
I BI O
IBIB
Type A
Type A
Type B
Type B
IAIB
Type AB
There are 3 alleles
for blood typemultiple alleles
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Codominance
R = allele for red flowers
W = allele for white flowers
red x white ---> red & white spotted
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Polygenic traits
Most traits are controlled by many
genes, not just one.
Examples: hair color and skin color.
There are several genes that control
them.
This is the reason that there are so
many different colors of hair and skin
in humans.
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Sex Linked Traits
Traits associated with particular
sexes are called sex-linked or
X-linked traits.
These are usually carried on the
X chromosome.
Females = XX
Males = XY
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1st 22 are Autosomes, the last pair
(XY) are sex chromosomes)
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Charts that show relationships
within a family
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AutosomalDominant
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SEX-LINKED
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SEX-LINKED
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Autosomal
-Dominant
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Huntington’s Disease
• Huntington's disease degenerative disease
that causes certain nerve cells in your brain
to waste away.
• you may experience uncontrolled movements,
emotional disturbances and mental
deterioration.
• The disorder was documented in 1872 by
American physician George Huntington.
• Fatal----ages:30-60
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Colorblindness
• Sex-linked trait
• Gene for color vision located on
the X chromosomes.
• Males are more likely to have
colorblindness because they have
only one X chromosome
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What do
you see?
The individual with normal color vision will see a 5
revealed in the dot pattern. An individual with
Red/Green (the most common) color blindness will
see
a
2
revealed
in
the
dots.
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Down Syndrome
• Three copies of chromosome #21.
• Symptoms: mental retardation and some physical deformities
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Down’s Syndrome – How do you get
3 copies of chromosome 21?
Nondisjunction – failure
of chromosomes to
separate properly
during cell division
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Cystic Fibrosis
• caused by a recessive
allele on chromosome
#7.
• Deletion of three
bases.
• Affects the body's
respiratory and
digestive systems.
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Hemophilia
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Queen Victoria’s Pedigree showing
Hemophelia
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Sickle Cell
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People who carry the tendency to
have sickle cell anemia are less
likely to die from malaria.
Gene Therapy
The insertion of healthy genes into an individual’s
cells or tissues to treat a disease.
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Example EOCT question:
What is nondisjunction?
A. failure of chromosomes to separate
during meiosis
B. failure of the cytoplasm to divide
properly
C. the insertion of a gene into a different
chromosome
D. the deletion of a gene from a
chromosome
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Which of the following shows how
information is transformed to make a
protein?
A DNA RNA  protein
B gene  chromosome protein
C cell respiration  ATP  protein
D ATP  amino acid  protein
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Information on mRNA is used to make a
sequence of amino acids into a protein by
which of the following processes?
A replication
B translation
C transcription
D transference
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Pea plants have seeds that are
either round or wrinkled. In this
cross, what will be the
phenotypic ratio of the offspring?
A
B
C
D
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50% RR and 50% Rr
25% RR, 50% Rr, and 25% rr
50% round seeds and 50% wrinkled seeds
100% round seeds
What is a source of
genetic variation?
A mutation
B adaptation
C replication
D transcription
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In Mendel’s experiments with
a single trait, the trait that
disappeared in the first
generation
and reappeared in the next
generation is called the
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A homozygous trait
B dominant trait
C recessive trait
D heterozygous trait