GENETICS-PATTERNS OF INHERITANCE
GENETIC TRAITS
1.
2.
3.
4.
5.
Dominant / Recessive Trait
a. mono-hybrid crosses
b. di-hybrid crosses
c. test cross
d. pedigree chart
Incomplete Dominance Trait
Co-dominant Trait
Multiple Allele Trait
Sex-linked Trait
Text Ref: Pgs. 314-317
Pg. 316 Visual Summary
“How to Make a Punnett Square” - GREAT HELP!
 Mono-hybrid Cross
 Di-hybrid Cross
PUNNETT SQUARE PRACTICE PROBLEMS
When solving a genetic trait inheritance problem using a Punnett square INCLUDE…
1. Write a key of all possible Genotypes
2. Write the Genotype of both parents
3. Determine the Gamete alleles
4. Place all possible gamete alleles on a Punnett square
5. Complete the Punnett square combining the gamete genotypes
6. Analyze the data (First generation)…
a.
Write the genotype ratio of offspring
b.
Write the phenotype ration of offspring
EXAMPLE
1. Genotype KEY
Plant Height: T= Tall
t = short
Cross:
Tt
TT, Tt
tt
x
Tt
2. Parent genotypes
Heterozygous X Heterozygous
Tt
T
3. Gametes
GaG
Parent genotypes
T
Tall
TT
Tt
Tall
t
Tt
Parent genotype
t
Tall
Tt
Short
tt
6. 6. Analyze data
Genotype: 25% homozyg. dom (TT)
50% heterozygous (Tt)
25% homozyg. Rec. (tt)
Phenotype: 75% Tall
25% Short
PUNNETT SQUARE PRACTICE PROBLEMS
Dominant / Recessive Traits
Text Ref: Pg. 316
A. Mono-hybrid Crosses
1. TRAIT: Pea Pod Shape:
(S) smooth shape (dominant)
(s)constricted shape(recessive)
CROSS: Heterozygous for smooth pods X Homozygous Recessive for constricted pods
2. TRAIT: Flower position:
(A) axial (dominant)
(a) terminal (recessive)
CROSS: Two plants that are Heterozygous for axial flowers
3.
TRAIT: Plant Height
(T) Tall plant
(t) Short plant
CROSS: One plant that is Homozygous tall with a Heterozygous
4.
Three-fourths of the plants produced by a cross between two unknown pea plants have
green pods and ¼ have yellow pods. What are the genotypes of the parents?
B. Di-hybrid Crosses
1. In fruit flies…
The gene for brown body color (B) is dominant to the gene for yellow body color (b). The
gene for long wings (L) is dominant to the gene for short wings (l).
CROSS :
A heterozygous brown, short winged male is bred to a yellow, homozygous long-winged female
2. In mice…
The ability to run normally is a dominant trait. Mice with this trait are called running mice
(R). The recessive trait causes mice to run in circles only. Mice with this trait are called
waltzing mice (r). Hair color is also inherited in mice. Black hair (B) is dominant over
brown hair (b).
CROSS :
A heterozygous running, heterozygous black mouse with a homozygous running, homozygous
black mouse.
3. Use the cross scenario from question 2 above.
CROSS :
A waltzing, brown mouse with a waltzing, brown mouse.
4. In humans…there is a disease called Phenylketonuria (PKU) which is caused by a recessive
allele. People with this allele have a defective enzyme and cannot break down the amino
acid phenylalanine. This disease can result in mental retardation or death.
Let “E” represent the normal enzyme.
Also in humans… is a condition called galactose intolerance or galactosemia, which is also
caused by a recessive allele. Let “G” represent the normal allele for galactose digestion. In
both diseases, normal dominates over recessive.
CROSS : A man who is heterozygous for both traits (EeGg) marries a woman who was
homozygous recessive for PKU and heterozygous for galactosemia.
What are their chances of having a child that is completely normal? Has just PKU?
Has just galactosemia? Has both diseases?
Incomplete Dominance Traits (Blending)
Text Ref: Pg. 319
Figure 11-12
1. In humans straight hair (SS) and curly hair (CC) are incomplete dominant traits, that result in
hybrids who have wavy hair (SC).
CROSS :
A curly hair female with a wavy haired male.
2. For some cats… the gene for tail length shows incomplete dominance. Cats with long tails (LL)
and those with no tails (NN) are homozygous for the respective allele. Cats with one long-tail
allele and one no-tail allele (LN) have short tails.
CROSS :
A long tail cat and a short tail cat.
3. Use the scenario above.
CROSS :
A two short tail cats.
4. Consider a cross between pure red and pure blue four o’clock flower in which neither color is
completely dominant.
CROSS :
F1 offspring X F1 offspring
Co-Dominant Traits
Text Ref: Pg. 319
(Both traits appear in the offspring)
NO PUNNETT SQUARES REQUIRED 
SIMPLY IDENTIFY THE PHENOTYPE OF THE OFFSPRING.
1. There is a breed of chickens where the trait for feather color is co-dominant.
CROSS: If one were to mate a white hen with a black rooster what phenotype would you expect
to see in the offspring?
2.
Roan fur in cattle is a codominant trait.
Cattle fur can be red (RR = all red hairs), white (WW = all white hairs), or roan (RW).
CROSS: If a red fur cow was bred with a white fur bull. Describe what would be the
phenotype of the roan fur offspring would look like?
3.
CROSS: Predict the phenotypic ratios of offspring when a homozygous white cow is crossed
with a roan bull.
Answers
Answers
Answers
Answers
Answers
Answers
Answers
Answers
A. Mono-hybrid Crosses
1. TRAIT: Pea Pod Shape:
(S) smooth shape (dominant) SS, Ss
(s)constricted shape(recessive) ss
CROSS: Heterozygous for smooth pods X Homozygous Recessive for constricted pods
Ss
ss
S
Ss
Ss
s
s
s
ss
ss
2/4 (50%) Ss = Smooth shape
2/4 (50%) ss = Constricted shape
2. TRAIT: Flower position:
(A) axial (dominant)
AA,Aa
(a) terminal (recessive) aa
CROSS: Two plants that are Heterozygous for axial flowers
Aa x Aa
A
A
AA
a
Aa
a
Aa
aa
3.
1/4 (25%) AA = Axial Flowers
2/4 (50%) Aa = Axial Flowers
¼ (25%) aa = Terminal Flowers
75% Axial Flowers / 25% Terminal
TRAIT: Plant Height
(T) Tall plant
TT, Tt
(t) Short plant tt
CROSS: One plant that is Homozygous tall with a Heterozygous
TT
Tt
T
T
T
TT
TT
t
Tt
Tt
2/4 (50%) TT = Tall Plant
2/4 (50%) Tt = Tall Plant
100% Tall Plants
4.
Three-fourths of the plants produced by a cross between two unknown pea plants have
green pods and ¼ have yellow pods. What are the genotypes of the parents?
Gg
X
Gg
3/4 (75%) Green Pods
1/4 (25%) Yellow Pods
TEST CROSS #2 - YES...YELLOW..
NO only (50%)
TEST CROSS #1 - YES Yellow (75%)
g
g
G
Gg
Gg
GG, Gg
gg
G
Gg
Gg
G
Gg
Gg
g
g
g
gg
gg
Test #3
YES… Yellow
YES… 75%
G g
G GG Gg
g Gg
gg
B. Di-hybrid Crosses
1. In fruit flies…
The gene for brown body color (B) is dominant to the gene for yellow body color (b). The
gene for long wings (L) is dominant to the gene for short wings (l).
CROSS :
A heterozygous brown, short winged male is bred to a yellow, homozygous long-winged female
Bb
ll
bb
LL
KEY
bL
bL
bL
bL
Brown Color= BB,Bb
Yellow Color = bb
Long Wings = LL, Ll
Short Wings = ll
Bl
BbLl
BbLl
BbLl
BbLl
Bl
BbLl
BbLl
BbLl
BbLl
bl
bbLl
bbLl
bbLl
bbLl
bl
bbLl
bbLl
bbLl
bbLl
8/16 (50%) BbLl =Brown body color with long wings
8/16 (50%) bbLl =Yellow body color with long wings
2. In mice…
The ability to run normally is a dominant trait. Mice with this trait are called running mice
(R). The recessive trait causes mice to run in circles only. Mice with this trait are called
waltzing mice (r). Hair color is also inherited in mice. Black hair (B) is dominant over
brown hair (b).
CROSS :
A heterozygous running, heterozygous black mouse with a homozygous running, homozygous
black mouse.
Rr
Bb
RR
BB
KEY
RB
Rb
rB
rb
Running
Waltzing
Black hair
Brown hair
RR,
Rr
rr
BB, Bb
bb
RrBb X
RRBB
RB
RB
RRBB
RRBb
RB
RrBB
RrBb
RB
25% RRBB, 25% RRBb, 25% RrBB, 25% RrBb
100% Running,
Black
3.
CROSS :
A waltzing, brown mouse with a waltzing, brown mouse.
rr
KEY
rb
rb
rb
rb
bb
Running
Waltzing
Black hair
Brown hair
RR,
Rr
rr
BB, Bb
bb
rrbb
X
rrbb
rb
rrbb
rb
rb
rr
bb
rb
100% rrbb
100% waltzing,brown
4. In humans…there is a disease called Phenylketonuria (PKU) which is caused by a recessive
allele. People with this allele have a defective enzyme and cannot break down the amino
acid phenylalanine. This disease can result in mental retardation or death.
Let “E” represent the normal enzyme.
Also in humans… is a condition called galactose intolerance or galactosemia, which is also
caused by a recessive allele. Let “G” represent the normal allele for galactose digestion. In
both diseases, normal dominates over recessive.
CROSS : A man who is heterozygous for both traits (EeGg) marries a woman who was
homozygous recessive for PKU and heterozygous for galactosemia.
What are their chances of having a child that is completely normal? Has just PKU?
Has just galactosemia? Has both diseases?
KEY
Normal enzyme
Defective enzyme(PKU)
Galactose digestive enz.
Galactose intolerance
EeGg X
EG
Eg
eG
eg
eG
EeGG
EeGg
eeGG
eeGg
1.
2.
3.
4.
EE,
Ee
ee
GG, Gg
gg
eeGg
eg
eG
EeGg
Eegg
eeGg
eegg
eg
3/8 normal child
3/8 just PKU
1/8 just galactosemia
1/8 both
diseases
1/8 EeGG
2/8 EeGg
1/8 eeGG
2/8 eeGg
1/8 Eegg
1/8 eegg
No PKU, No galactosemia
No PKU, No galactosemia
PKU, No galactosemia
PKU, No galactosemia
No PKU, Yes galactosemia
Yes PKU, Yes galactosemia
Incomplete Dominance Traits (Blending)
Text Ref: Pg. 319
Figure 11-12
1. In humans straight hair (SS) and curly hair (CC) are incomplete dominant traits, that result in
hybrids who have wavy hair (SC).
CROSS :
KEY:
A curly hair female with a wavy haired male.
CC
SC
Straight Hair
SS
Curly Hair
CC
Wavy Hair-Blend SC
S
C
SC
C
SC
C
CC
CC
2/4 (50%) SC = Wavy Hair
2/4 (50%) CC = Curly Hair
2. For some cats… the gene for tail length shows incomplete dominance. Cats with long tails (LL)
and those with no tails (NN) are homozygous for the respective allele. Cats with one long-tail
allele and one no-tail allele (LN) have short tails.
CROSS :
KEY:
A long tail cat and a short tail cat.
LL
LN
Long Tail
No Tail
Short Tail-Blend
L
L
LL
N
LN
L
LL
LN
LL
NN
LN
2/4 (50%) LL = Long Tail
2/4 (50%) LN= Short Tail
3. For some cats… the gene for tail length shows incomplete dominance. Cats with long tails (LL)
and those with no tails (NN) are homozygous for the respective allele. Cats with one long-tail
allele and one no-tail allele (LN) have short tails.
CROSS :
KEY:
A two short tail cats.
LN x LN
Long Tail
No Tail
Short Tail-Blend
L
L
LL
N
LN
N
LN
NN
LL
NN
LN
1/4 (25%) LL = Long Tail
2/4 (50%) LN= Short Tail
1/4 (25%) NN = No Tail
4. Consider a cross between pure red and pure blue four o’clock flower in which neither color is
completely dominant.
CROSS :
KEY:
R
B
F1 offspring X F1 offspring
RB x
RB
Red Flower
Blue
Purple-Blend
B
R
RB
R
RB
B
RB
RB
R
RR
RB
B
RB
BB
RR
BB
RB
F1- 100% RB (PURPLE)
1/4 (25%) RR - Red
2/4 (50%) RB-Purple
1/4 (25%) BB - Blue
Co-Dominant Traits
Text Ref: Pg. 319
(Both traits appear in the offspring)
NO PUNNETT SQUARES REQUIRED 
SIMPLY IDENTIFY THE PHENOTYPE OF THE OFFSPRING.
1. There is a breed of chickens where the trait for feather color is co-dominant.
CROSS: If one were to mate a white hen with a black rooster what phenotype would you expect
to see in the offspring?
ANSWER:
2.
(parents) WW x BB
(offspring) BW = genotype
Black and white mixed hair = phenotype
Roan fur in cattle is a codominant trait.
Cattle fur can be red (RR = all red hairs), white (WW = all white hairs), or roan (RW).
CROSS: If a red fur cow was bred with a white fur bull. Describe what would be the
phenotype of the roan fur offspring would look like?
ANSWER:
3.
(parents) RR x WW
(offspring) RW = genotype
Red hair with white patches OR
White hair with red patches = phenotype
CROSS: Predict the phenotypic ratios of offspring when a homozygous white cow is crossed
ANSWER:
with a roan bull.
(parents) WW x RW
(offspring) genotypes
50% WW
50% RW
=
=
phenotypes
All white offspring
Red and white mixed hair-roan