SOLVING GENETICS PROBLEMS
Honors Biology
Unit 5
Powerpoint #2 / Chapter 11
SOLVING GENETICS PROBLEMS
Phenotype: physical appearance
Example: Tall, Short, Blonde, Red,
Brown Eyes
Genotype: genes in the DNA (alleles)
Example: TT bb Rr Bb
ALLELE: A VARIETY OF A GENE
A gene for hair color could have
the allele: _______
for Brown hair
B
or _______
for Blonde hair
b
 A gene for flower color could
have allele: ______for
blue flower
B
or ________
for red flower
b
 A gene for height could have the
T
t
alleles: _______
for tall or _______
for short

SOLVING GENETICS PROBLEMS

Dominant: An allele that
causes its phenotype if at least
1 is present
Examples: TT, Tt (Tall)

Recessive: An allele that
causes a phenotype only when
there are 2 alleles
Example: tt (short)
SOLVING GENETICS PROBLEMS
Homozygous: organism with 2
identical alleles for a trait
(TT or tt)
Heterozygous: organism with 2
different alleles for a trait
(Tt)
SOLVING GENETICS PROBLEMS
Homozygous dominant: has
2 dominant alleles (TT)
Homozygous recessive: has 2
recessive alleles (tt)
A
B
C
D
Plant A:
a. Phenotype: Tall
b. Genotype: TT
E
F
G
H
A
B
C
D
E
Plant B:
a. Phenotype: short
b. Genotype: tt
F
G
H
A
B
C
D
Plant C:
a. Phenotype: Tall
b. Genotype: Tt
E
F
G
H
SOLVING GENETICS PROBLEMS
Genetics Problems
Goal: to predict the traits of offspring
SOLVING GENETICS PROBLEMS
Genetics Problems
Goal: to predict the traits of offspring
1.
Identify trait(s) and assign a letter to
each (capital letter for dominant, lower
case letter for recessive)
SOLVING GENETICS PROBLEMS
Genetics Problems
Goal: to predict the traits of offspring
1.
Identify trait(s) and assign a letter to
each (capital letter for dominant, lower
case letter for recessive)
2.
Determine parents’ genotypes
SOLVING GENETICS PROBLEMS
Genetics Problems
Goal: to predict the traits of offspring
1.
Identify trait(s) and assign a letter to
each (capital letter for dominant, lower
case letter for recessive)
2.
Determine parents’ genotypes
3.
Draw Punnett square and fill in
SOLVING GENETICS PROBLEMS
Genetics Problems
Goal: to predict the traits of offspring
1.
Identify trait(s) and assign a letter to
each (capital letter for dominant, lower
case letter for recessive)
2.
Determine parents’ genotypes
3.
Draw Punnett square and fill in
4.
Determine the probabilities for offspring
of each genotype and phenotype
SOLVING GENETICS PROBLEMS
Example:
In pea plants, the gene for tall height is
dominant to the gene for short height. A
short pea plant is cross pollinated with a
true breeding tall pea plant.
1.
2.
Assign letters:
tall = T short = t
Parents’ genotypes
True breeding tall: TT
True breeding short = tt
SOLVING GENETICS PROBLEMS
3. Draw Punnett Square
SOLVING GENETICS PROBLEMS
3. Draw Punnett Square
t
T
T
t
SOLVING GENETICS PROBLEMS
3. Draw Punnett Square
t
t
T
Tt
Tt
T
Tt
Tt
SOLVING GENETICS PROBLEMS
4. Calculate probabilities
TT = _____
Tt = ________
tt = _________
Tall = _________
Short = _________
t
t
T
Tt
Tt
T
Tt
Tt
SOLVING GENETICS PROBLEMS
4. Calculate probabilities
10) TT = 0/4
Tt = 4/4
tt = 0/4
11) Tall = 4/4
Short = 0/4
t
t
T
Tt
Tt
T
Tt
Tt
IDENTIFY TRAIT(S) AND ASSIGN A LETTER TO
EACH (CAPITAL LETTER FOR DOMINANT, LOWER
CASE LETTER FOR RECESSIVE)
Examples:
In guinea pigs, the gene for black fur is dominant to the
gene for white fur.
black = ____
white = ____
IDENTIFY TRAIT(S) AND ASSIGN A LETTER TO
EACH (CAPITAL LETTER FOR DOMINANT, LOWER
CASE LETTER FOR RECESSIVE.
Examples:
In guinea pigs, the gene for black fur is dominant to the
gene for white fur.
DETERMINE PARENTS’ GENOTYPES.
Example:
In guinea pigs, the gene for black fur is
dominant to the gene for white fur. A white
guinea pig and a hybrid black guinea pig
produce 20 offspring. Find the probability
of offspring genotypes and phenotypes.
1. Black: ___White: ___
2. White guinea pig: ___
Hybrid black guinea pig: ___
DETERMINE PARENTS’ GENOTYPES.
Example:
In guinea pigs, the gene for black fur is
dominant to the gene for white fur. A white
guinea pig and a hybrid black guinea pig
produce 20 offspring. Find the probability
of offspring genotypes and phenotypes.
1. Black: B White: b
2. White guinea pig: ___
Hybrid black guinea pig: ___
DETERMINE PARENTS’ GENOTYPES.
Example:
In guinea pigs, the gene for black fur is
dominant to the gene for white fur. A white
guinea pig and a hybrid black guinea pig
produce 20 offspring. Find the probability
of offspring genotypes and phenotypes
1. Black: B White: b
2. White guinea pig: bb
Hybrid black guinea pig: ___
DETERMINE PARENTS’ GENOTYPES.
Example:
In guinea pigs, the gene for black fur is
dominant to the gene for white fur. A white
guinea pig and a hybrid black guinea pig
produce 20 offspring. Find the probability
of offspring genotypes and phenotypes.
1. Black: B White: b
2. White guinea pig: bb
Hybrid black guinea pig: Bb
SOLVING GENETIC PROBLEMS
3. Draw Punnett Square
B
b
b
Bb
bb
b
Bb
bb
SOLVING GENETICS PROBLEMS
4. Calculate probabilities
BB = 0/4
Bb = 2/4 (50%)
bb = 2/4 (50%)
How many of the babies will
Probably be Black = 10
How many of the babies will
Probably be White = 10
B
b
b
Bb
bb
b
Bb
bb
HUMANS CAN HAVE UNATTACHED EARLOBES (PICTURE A) OR
ATTACHED EARLOBES (PICTURE B). ATTACHED EARLOBES ARE
DOMINANT. USE THE LETTER ‘E’ TO COMPLETE THE
FOLLOWING QUESTIONS.
Ear Lobes
HUMANS CAN HAVE UNATTACHED EARLOBES (PICTURE A) OR
ATTACHED EARLOBES (PICTURE B). ATTACHED EARLOBES ARE
DOMINANT. USE THE LETTER ‘E’ TO COMPLETE THE
FOLLOWING QUESTIONS.
1)
A mother is homozygous dominant
for ear type and a father is
heterozygous:
EE
a) What is the mother’s genotype? ______
Ee
Father’s genotype? ____
b) What are their phenotypes?
Mother: ___________
Attached
Father: _________
Attached
1) A MOTHER IS HOMOZYGOUS DOMINANT FOR
EAR TYPE AND A FATHER IS HETEROZYGOUS:

Draw a punnett square:
E
e
E
EE
Ee
E
EE
Ee
1) A MOTHER IS HOMOZYGOUS DOMINANT FOR
EAR TYPE AND A FATHER IS HETEROZYGOUS:
d: What are the chances
they will have children
that are:
Homozygous Dominant: E
____
50%
Heterozygous:
E
____
50%
Homozygous Recessive:
____
0%
E
e
EE
Ee
EE
Ee
TONGUE ROLLING: DOMINANT

If a mother can roll her tongue and a father
can not.

What do we know about their genes?
TONGUE ROLLING: DOMINANT
 If
a mother can roll her tongue and a
father can not.

What do we know about their genes?
Mother:
RR or Rr
_______
Father:
rr only
_______
2) B. IF YOU KNOW THAT THEY HAVE 2 CHILDREN,
ONE THAT CAN ROLL AND ONE THAT CAN NOT. WILL
THAT GIVE YOU MORE INFO ABOUT THE PARENT’S
GENOTYPES?
r
R
Yes!
c. Draw a punnett
square:
r
Rr
rr
r
Rr
rr
TONGUE ROLLING: DOMINANT
d. Which people in the family would be
considered hybrids?
Mom and the child that can roll
their tongue
e. Are their any genotypes that this mother
and father can not produce in their offspring?
Why or why not?
Yes, they can not produce a Homozygous
Dominant (RR) child because the father
only has recessive genes (r) to pass on
CO AND INCOMPLETE
DOMINANCE
DEFINITIONS
Co-dominance:
Both alleles are dominant and
contribute to the phenotype of
a heterozygous individual
 Incomplete Dominance:
One allele is NOT completely
dominant over the other
SOLVE THE FOLLOWING CROSSES:
CO-DOMINANCE
3.
In Cows the trait for coat (fur) color is
expressed by R for Red fur and W for
white fur. The hybrid of the two is
called a Roan color (RW).
a) Describe what you think the Roan cow’s fur
will look like:
CO-DOMINANCE
FILL IN THE PUNNETT SQUARE
Genotypes
R
Phenotypes
R
W RW RW
W RW
RW
2. R= RED FUR
W= WHITE FUR
 What
do you think a RW cow will look like:
____________________
Red and White spots
 If the mother cow is homozygous red for fur
color. What is her genotype: _____
RR
Phenotype?________________
Red Fur
 If the dad is homozygous white for fur color.
What is his genotype: _____
WW
Phenotype?________________
White Fur
 What percentage of the offspring will be
RW: ______________
100%
SOLVE THE FOLLOWING CROSSES:
CO-DOMINANCE
4.
In mushrooms there is a gene for
Purple Spots (P) and a gene for
Green spots (G). Cross a
Homozygous purple with a
Homozygous Green.
a) What do you think their offspring will
look like? Genotype? Phenotype?
b) What will the genotype and phenotype
percentages be in the F2 when you
cross two from the F1 generation.
PHENOTYPES
PP
GG
GP
INCOMPLETE DOMINANCE
 The
heterozygous (Rr) Does not look
like the Homozygous recessive (rr) or
the homozygous dominant (RR).
INCOMPLETE DOMINANCE
1.
In flowers there is a gene for Red (R)
which has incomplete dominance to
the recessive color white (r). The
heterozygote plant produced by a
white and red flower is pink
RR
rr
Rr
SOLVE THE FOLLOWING CROSSES:
INCOMPLETE DOMINANCE
B= BLACK (INCOMPLETE DOMINANCE)
B = YELLOW (RECESSIVE)
 What
is the genotype for a dog that is Black
: ______
BB
 What is the genotype for a dog that is
Yellow :_____
bb
 What is the genotype for a dog that is
Brown: ______
Bb
 Show a cross between a Brown dog and a
yellow dog.
FILL IN THE PUNNETT SQUARE
Genotypes
Phenotypes
B
b
Bb
bb
b Bb
bb
b
WHAT PERCENTAGE OF THE PUPPIES ARE
 BB=_________
0%
 Bb=__________
50%
 bb=
__________
50%
B = BLACK FUR (INCOMPLETE DOMINANCE)
B= WHITE FUR (RECESSIVE)
 What
do you think the genotype would
be for the mother sheep if she has
bb
white fur: ____________
 What do you think the genotype would
be for the father sheep if he has black
fur:_______________
BB
 What color would a Bb sheep be:
__________________________
Gray
FILL IN THE PUNNETT SQUARE
Genotypes
B
B
Bb
Bb
b Bb
Bb
b
Phenotypes
WHAT PERCENTAGES WILL THE F1 BE:
BB: _______%
0
 Bb: ________%
100
 bb: ________%
0
 Black:_________%
0
 White:_________%
0
 Hybrid: ________%
100
