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SOLVING GENETICS PROBLEMS
Honors Biology
Unit 5
Powerpoint #1 / Chapter 11
TRAITS
 What
are some of your traits?
 Where did they come from?
 Do you look like one of your parents,
a combination, or neither?
 Do certain traits “run” in your
family? Or pop up after skipping a
generation
 What traits are common in our
class? why do you think that is?
Mendel’s Pea plant Observations
Mendel’s Experiment
P Generation
Tall
TT
F1 Generation
Short
tt
Tall
Tall
Tt
Tt
F2 Generation
Tall
TT
Tall
Tt
Tall
Tt
Short
tt
HYBRID: OFFSPRING OF CROSSES BETWEEN
PARENTS WITH DIFFERENT TRAITS.
Example: Cross pollinate a true-breeding
purple flower and a true breeding white
flower. Seedlings=hybrid (even though they
are purple)
X
=
HYBRID CARS
Gas + Electric
TERMINOLOGY
Gene: segment of DNA
that determines a trait
Alleles: different forms of a gene
(ex: Height: tall allele, or short
allele)
Allele
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) (aka Hybrid)
SOLVING GENETICS PROBLEMS
Homozygous dominant
has 2 dominant alleles (TT)
Homozygous recessive
has 2 recessive alleles (tt)
SOLVING GENETICS PROBLEMS
Phenotype: physical appearance
Example: Tall, Short, Blonde, Red,
Brown Eyes
Genotype: genes in the DNA (alleles)
Example: TT bb Rr Bb
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 *remember 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
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
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
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 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
Tall = 4/4
Short = 0/4
what % will be tall? : 100%
t
t
T
Tt
Tt
T
Tt
Tt
PROBLEM #1
 Brown
hair is dominant to blonde
hair. If two heterozygous brown hair
parents have 8 children, how many
of them do you expect to have blonde
hair?
 Use the letter B to solve the punnett
square
 Parents Genotypes: Bb
SOLVING GENETIC PROBLEMS
3. Draw Punnett Square
B
b
B
BB
Bb
b
Bb
bb
SOLVING GENETICS PROBLEMS
4. Calculate probabilities
BB = ¼ (25%)
Bb = 2/4 (50%)
bb = 1/4 (25%)
How many do you expect
to have blonde hair?
2
B
b
B
BB
Bb
b
Bb
bb
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 GENETICS PROBLEMS
B
b
b
Bb
bb
How many of the babies will b
Probably be Black =
10
How many of the babies will
Probably be White =
10
Bb
bb
4. Calculate probabilities
BB = 0/4
Bb = 2/4 (50%)
bb = 2/4 (50%)
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
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
Co and Incomplete
Dominance
DEFINITIONS
Co-dominance:
Both alleles are
dominant and
contribute to the
phenotype of a
heterozygous
individual
SOLVE THE FOLLOWING CROSSES:
CO-DOMINANCE
3.
In Cows the trait for coat (fur)
color is expressed by FR for Red
fur and FW for white fur. The
hybrid of the two is called a Roan
color (FRFW)
a) Describe what you think the Roan
cow’s fur will look like:
CO-DOMINANCE
2. FR= RED FUR
FW= WHITE FUR
do you think a FRFW cow will look
like:
Red____________________
and White spots
 If the mother cow is homozygous red for fur
FRFR
color. What is her genotype: _____
Phenotype?________________
Red Fur
 If the dad is homozygous white for fur color.
FWFW
What is his genotype: _____
Phenotype?________________
White Fur
 What percentage of the offspring will be
100%
FRFW: ______________
 What
FILL IN THE PUNNETT SQUARE
Genotypes
W
F
R
F
R
F
R
W
F F
R
W
F F
Phenotypes
W
F
R
W
F F
R
W
F F
SOLVE THE FOLLOWING CROSSES:
CO-DOMINANCE
In mushrooms there is a gene for
Purple Spots (SP) and a gene for Green
spots (SG). 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
S P SP
SGSG
S P SG
SICKLE CELL HEMOGLOBIN ALLELE IS CODOMINANT TO NORMAL HEMOGLOBIN ALLELE
HbA HbS
SICKLE CELL: CROSS TWO HETEROZYGOUS
INDIVIDUALS
25%
 Normal Hemoglobin: _____
50%
Cell Trait: _____
25%
 Sickle Cell Anemia: _____
 Sickle
A
Hb
S
Hb
A
Hb
HbA
HbA
HbA HbS
S
Hb
HbA
HbS
HbS HbS
SICKLE CELL: AUTOSOMAL CO-DOMINANT
DISORDER

Sickle shaped cells are resistant to Malaria
S
Hb
and Malaria Frequency
INCOMPLETE DOMINANCE
One
allele is NOT completely
dominant over the other
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 white fur:
____________
bb
 What do you think the genotype would be for
the father sheep if he has black
BB
fur:_______________
 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

BB: ________%
Bb: ________%
bb: ________%
Black:_______%
B
b
B
b
BB
Bb
Bb
bb
BB: 25%
Bb: 50%
bb: 25%
Black: 25%
B
b
B
b
BB
Bb
Bb
bb