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INCOMPLETE DOMINANCE

With incomplete dominance, a
cross between organisms with two
different phenotypes produces
offspring with a third phenotype
that is a blending of the parental
traits.
INCOMPLETE DOMINANCE

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When the phenotype of the
heterozygous is intermediate
between the two homozygous
Neither allele is dominant/recessive
over the other. Neither allele will
express itself---therefore NO
capital or lower case letters
INCOMPLETE DOMINANCE
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EX:
Snapdragon
flowers.
Red flowers
White flowers
Pink Flowers
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When working
these problems
it becomes
essential to
make a key
Red (RR)
White (WW)
Pink (RW)
INCOMPLETE DOMINANCE

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Cross a Red Snapdragon
flower with a White
Snapdragon flower.
Set up the Punnett Square and
give me both pheno and geno
Ratios.
INCOMPLETE DOMINANCE
INCOMPLETE DOMINANCE

Phenotypic
Ratio
100% Pink
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Genotypic
Ratio
100% RW
INCOMPLETE DOMINANCE

You cross two pink flowers
and give me both phenotypic
and genotypic ratios.
CO-DOMINANT ALLELES
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Where both alleles express
themselves fully.
With Co-dominance, a cross
between organisms with two
different phenotypes produces
offspring with a third phenotype.
This third phenotype has BOTH
parental traits expressed.
CO-DOMINANT ALLELES

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This is most commonly seen in
chickens. Cross a black chicken with a
white chicken you get what is called a
speckled chicken
NOT GRAY…but both alleles (black and
white) fully express themselves so the
chicken has both types of feathers.
CO-DOMINANT ALLELES

White cow crossed with a Red Bull
CO-DOMINANT ALLELES
Roan Cow…. Roan refers to cows that
have red coats with white blotches.
CO-DOMINANT ALLELES
A white horse crossed with a black stallion
CO-DOMINANT ALLELES
A gray horse…but upon closer inspection it has
hairs that are both black and hairs that are
white.
POLYGENIC TRAITS
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More than one allele pair
controls a single trait—
Ex: Skin Color—Several
different allele pairs attribute
to the overall phenotype—
Tone, distribution, etc
MULTIPLE ALLELES
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A population might have more than two
alleles for a given gene.
In this case you have to think of a gene
as a segment of your DNA that controls
a trait.
You have more than 2 choices for an
allele for each trait.
Even if more than two alleles exist in a
population, any given individual can
have no more than two of them.
MULTIPLE ALLELES

Ex: Blood type, Rabbit Fur,
Labrador Retriever Coat Color
MULTIPLE ALLELES

In Labs, coat color is determined by one
gene with four different alleles. Five
different colors result from a
combination of these alleles.
Phenotype
Possible Genotypes
BBEE
BbEE
BBEe
BbEe
bbEE
bbEe
BBee
Bbee
bbee
Multiple Alleles- Blood Type
Blood Type of
Preferred
Permissible
Recipient
Blood Type of Blood Type of
Donor
Donor
A
A
A, O
B
B
B, O
AB
AB
AB, A, B, O
O
O
O
Multiple Alleles- Blood Type
Multiple Alleles-Rabbit Fur
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Coat color in rabbits
is determined by a
single allele pair that
has at least four
different alleles.
Full(C), Chinchilla (Ch),
Himalayan (h),
Albino (c)
SEX CHROMOSOMES

We already know
that each human
has 46
chromosomes
which means they
have 23
homologous
pairs.

The 23rd Pair is
different. It
determines the
sex of the
individual.
SEX CHROMOSOMES
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Homologous
Pairs
1-22 are called
Autosomes
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The 23 pair
often called the
Sex
Chromosome.
FEMALE SEX CHROMSOMES
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Female 23rd
Chromosome
is represented
by XX.
MALE SEX CHROMSOMES

The 23
Chromosome
on the male is
represented
with a XY.
SEX-LINKED TRAITS

Genes that are carried by either
sex chromosome are said to be
Sex-linked Traits.
SEX-LINKED TRAITS
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Scientist discovered this linkage
when studying fruit flies
(Drosophilia). Through many
experiments scientist soon
concluded eye color of these flies
were determined by the sex
chromosome.
SEX-LINKED TRAITS
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Often an allele
for a trait can
be found on the
X but not on
the Y
chromosome.
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The Y
chromosome on
the male
carries little or
NO genetic
information.
SEX-LINKED TRAITS
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WHEN WORKING ANY SEXLINKED TRAIT YOU MUST
ALWAYS WRITE IT OUT……
XX x XY
You still have dominant and
recessive alleles.
SEX-LINKED TRAITS
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Eye color in fruit flies is a sex-linked
trait where Red eyes is dominant over
White eyes. (This trait is carried on the
X chromosome)
Cross a heterozygous Red eyed female
with a red eyed male.
SEX-LINKED TRAITS
Practice Problems
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Cross a heterozygous Red eyed female
with a red eyed male.
Cross a homozygous Red eyed female
with a white eyed male.
Allow the F1 generation male/female to
cross.
Show me Cross, Punnett Square, and
Phenotypic and Genotypic Ratio
SEX-LINKED TRAITS

Most sex-linked
traits are carried
on the X
chromosome.
Therefore the
female will carry
two and the male
will only carry
one.

However, some
sex-linked traits
are carried on the
Y…but only a
few!!
Sex chromosomes can
carry other genes
Y-LINKED GENES:
Genes carried on Y chromosome
EX:
Hairy pinna
Y linked
males.
_________genes
only show up in _______
SEX-LINKED TRAITS
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Colorblindness
Hemophilia
Duchenne Muscular Dystrophy
Fragile X Syndrom
Sex chromosomes can
carry other genes
X-LINKED GENES:
Genes carried on
the X chromosome
EX: _____________
Hemophilia
_____________
Colorblindness
Duchenne Muscular Dystrophy
_________________________
SEX-INFLUENCED TRAITS
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(NOT located on X or Y chromosome)found in both sexes but expressed
differently.
Baldness-caused by autosomal allele
that is dominant in men due to the
presence of testosterone. It is
recessive trait in women.
Index finger length- Dom/fem Rec/Mal
SEX-LIMITED TRAITS
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Sex-limited traits are
autosomal traits that are
expressed in only one sex (In
normal conditions)
Ex: Breast, Beards, Breast
milk.
TESTCROSS
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Testcross- one way to determine
the genotype of an unknown
genotype is to cross it with a
known genotype (usually recessive)
TESTCROSS
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A breeder is
considering using
this dog to produce
offspring. However
the owner is unsure
if the dog is a
possible carrier of a
common hearing
problem. She
knows that he has
normal hearing.
What can she do?
Carrier

A carrier is a
heterozygous
individual. They
do NOT have the
trait but do have
the possibility to
pass it to their
offspring.
Dd
TESTCROSS
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When performing
a test cross you
would cross the
unknown
genotype with a
known…usually a
homozygous
recessive.
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Many breeders
will rely on a
testcross to
determine if they
are dealing with a
pure breed or a
hybrid.
PEDIGREE
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A graphic representation of
an individuals family tree.
PEDIGREE
CHART
Males =
Females =
Has trait =
Carrier =
KAROTYPE
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A photograph that shows an individuals
chromosomes in homologous pairs.
Usually done by collecting white blood
cells-stimulating mitosis and capture the
information.
Karotype can be used to find any
chromosomal abnormality.
KAROTYPE
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Most abnormalities are called by
Nondisjuction- the failure of one or
more chromosomes pairs to separate
during meiosis.
Down Syndrome
Klinefelter Syndrome
Turner Syndrome