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Take notes on the following slides on
your foldable.
on
whator
weRed
have
learned, what
White
Offspring,
Right?
offspring phenotypes
would you expect from
Not necessarily…
a cross between these two horses?
 Based
White Horse
Red Horse
Strawberry Roan
 How
did this happen?
Most of the time, traits display more
complex patterns of heredity than the simple
dominant-recessive pattern
 What
is the simple dominant-recessive
pattern known as?
Mendelian Genetics
Let’s look at Mendelian Genetics one more
time…and then let’s look at the other
patterns of inheritance!
 Again,
Mendelian genetics shows a pattern
where a clear dominant trait masks a
recessive trait.
 Cleft
chins, dimples, and freckles are all
examples of traits that follow Mendelian
patterns.
Punnett Square
Dimples (D) are dominant over no dimples (d)
Cross two parents that are heterozygous for
dimples. Complete the ratios for genotype
and phenotype.
Genotype: 1:2:1
D
d
D
DD
Dd
d
Dd
dd
Phenotype: 3:1

Occurs when the
heterozygous
allele combination
results in a blend
of the dominant
and recessive
trait.

Remember the
horses…
 Straight,
wavy and curly hair is one
example of incomplete dominance.
 Another
example is carnation color.
If the red and white alleles are
both present, the resulting
offspring will be pink (a blend of
red and white).
Punnett Square
 Red flower color (R) is
incompletely dominant
over white flower color
(r) in carnations.

Cross two parents that
are heterozygous for
flower color. Complete
the ratios for genotype
and phenotype.
R
r
R
RR
Rr
r
Rr
rr
Genotype: 1:2:1
Phenotype:1:2:1
 Occurs
when both alleles are expressed when the
heterozygous allele combination is present.
 Not a Blend!!
 Human blood is an example of co-dominance. A
and B alleles are both dominant over the
recessive allele, O. If both the A and B alleles are
present, both will be expressed.
Punnett Square
 Cross two parents that are co-dominant for
blood type. Give the ratios for genotype and
phenotype.
Genotype: 1:2:1
IA
IB
IA
IAIA
IAIB
IB
IAIB
IBIB
Phenotype:1:2:1
 Occurs
Only females
when acan
trait
beiscarriers
passed of
onX-Linked
from
generation
traits. Whattoisgeneration
a carrier? on one of the sexdetermining chromosomes (X, Y)
Why can’t males be carriers of X-Linked
traits?
 The dominant and recessive representative
alleles are written as superscripts on the X and
Y.
X R XR
XR Xr
XrXr
XRY
XrY
Punnett Square
 Cross a female carrier for colorblindness with
a normal male. List the possible phenotypes.
B – not affected
b - affected
Possible Phenotypes:
Normal Female
Carrier Female
Normal Male
Colorblind Male
XB
Xb
XB
XBXB
XBX b
y
XBy
Xby
What does Poly mean?
So POLY GENIC means MANY GENES!!!
Many
Genic looks like?
Genes!
 Occurs when several genes influence a trait
 The
genes may be on the same chromosome
or on different chromosomes
 Eye
color, height, weight, and hair and skin
color are all polygenic traits.
How many
 Genes
with three or
possible
more
alleles are
genotypes
for said to
have
multiple alleles.
blood?
6
How many
possible
 Human
blood has 3
phenotypes?
alleles:
A, B, and O.
4
ii
Punnet Square
Cross a parent with an IAIO genotype with a parent
that has the genotype IBIO for blood.
List the possible phenotypes.
Possible Phenotypes:
Type AB Blood
Type A Blood
Type B Blood
Type O Blood
IA
IO
IB
IAIB
IBIO
IO
IAIO
IOIO