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Mendelian Exceptions
Chapter 11
Section 3
Mendel’s Principles Revisited
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Inheritance of biological
_____________ is determined by
characteristics
individual units known as genes
______.
During sexual reproduction, genes are
offspring
passed from parents to _________.
Two or more forms of the gene for a
trait exist, some forms of the
single _____
gene may be _________
dominant and others
may be recessive.
Mendel’s Principles Revisited
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Organisms typically have ____copies
of
two
each gene, (one from each _______)
parent
An organism’s _____
pair of genes (2 alleles)
are segregated from each other when
gametes are formed.
________
genes usually
Alleles for different ______
independently of one
segregate _____________
another. (through meiosis)
(Law of Independent Assortment)
Independent Assortment in Peas
9 Round yellow
__
__
3 Round green
3 Wrinkled yellow
__
__
1 Wrinkled green
Incomplete Dominance

In incomplete dominance, neither allele is
dominant so there is a blending of
__________
traits when two different alleles for the
______
same trait occur together.

Colors blend together
heterozygous
(______________
individuals =
3rd phenotype)

red
pink
white
Incomplete Dominance

RR
In Four O’ Clocks, if you cross a red _____
WW
(which is always pure) with a white _____
(that is also always
pure) , you get a
RW (which
pink _____
is always hybrid /
heterozygous
RW
RW
RW
RW
Incomplete Dominance


RR and blue
In another flower, if red ____
BB flowers are crossed, they
____
RB flower
produce a 3rd purple ____
What would be the genotype ratio and
phenotype ratio if you crossed two
purple flowers?
Incomplete Dominance
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Cross of two purple flowers
RB X ____
RB
____
What are gamete possibilities?
R
genotype ratio
RR
1RR : 2RB : 1BB
R
red
phenotype ratio
1red : 2 purple : 1 blue
RB
B
purple
Can you have a
heterozygous red or
no
hybrid blue flower? ___
B
RB
purple
BB
blue
Codominance

alleles contribute to the
Both _______
phenotype of the organism by showing
up simultaneously (at the
same time) in heterozygous
individuals.
 In cattle and horses, if you
red (RR)
cross a pure ____
with a pure ______
white (WW),
you get (RW) which
roan
produces the color _____.
Codominance


These cattle or horses actually have both
red and white hairs intermixed, or are
phenotype
spotted. Roan is a third ___________.
If you cross a roan with a white…
R
W
W
RW
roan
WW
white
W
RW
roan
WW
white
Codominance
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Andalusian chickens also show this
pattern of inheritance.
If you cross a black (BB) chicken
With a white (WW) chicken
You get black+white speckled (BW) chicken
Multiple Alleles

In this pattern of inheritance, the genes
two alleles controlling
have more than _____
them and are therefore said to have
multiple alleles. No individual has more
two alleles, but there are more
than _____
two possible alleles in a
than _____
trait will be expressed
population, so a ______
in more than two forms.
Multiple Alleles
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Blood type in humans is an example of
this inheritance pattern.
Phenotype Genotype
four
The ______ different
blood groups:
A
AA or AO
A, B, O, and AB
B
BB or BO
Are produced
three different
by ______
AB
AB only
alleles:
O
OO only
A, B, and O
Multiple Alleles

Examples of Blood type crosses
Polygenic Traits

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Traits controlled by two or more genes
Show a wide range of phenotypes
The phenotype
is produced by
the interaction
of more than
1 pair
________
of genes.
Polygenic Traits



polygenic traits,
These are called ___________
many genes”.
which means “having _______
eye color,
In humans, _____
skin color,
_____
Polygenic Traits




polygenic traits,
These are called ___________
many genes”.
which means “having _______
eye color,
In humans, _____
skin color,
_____
hair color
and _____
Polygenic Traits

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
polygenic traits,
These are called ___________
many genes”.
which means “having _______
eye color,
In humans, _____
skin color,
_____
hair color
and _____
are just a few of
the many traits
controlled by
__________
many genes.