Solving Genetics Problems
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SOLVING GENETICS PROBLEMSHonors BiologyUnit 5Powerpoint #2 / Chapter 11
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SOLVING GENETICS PROBLEMS
Phenotype: physical appearanceExample: Tall, Short, Blonde, Red, Brown Eyes
Genotype: genes in the DNA (alleles)
Example: TT bb Rr Bb
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ALLELE: A VARIETY OF A GENE A gene for hair color could
have the allele: _______ for Brown hair or _______ for Blonde hair
A gene for flower color could have allele: ______for blue flower or ________ for red flower
A gene for height could have the alleles: _______ for tall or _______ for short
Bb
Bb
T t
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Dominant: An allele that causes its phenotype if at least 1 is presentExamples: TT, Tt (Tall)
Recessive: An allele that causes a phenotype only when there are 2 allelesExample: tt (short)
SOLVING GENETICS PROBLEMS
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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)
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Homozygous dominant: has 2 dominant alleles (TT)
Homozygous recessive: has 2 recessive alleles (tt)
SOLVING GENETICS PROBLEMS
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A B C D E F G H
Plant A: a. Phenotype: b. Genotype:
Tall
TT
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A B C D E F G H
Plant B: a. Phenotype: b. Genotype:
short
tt
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A B C D E F G H
Plant C: a. Phenotype: b. Genotype:
Tall
Tt
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SOLVING GENETICS PROBLEMSGenetics Problems
Goal: to predict the traits of offspring
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SOLVING GENETICS PROBLEMSGenetics Problems
Goal: to predict the traits of offspring1. Identify trait(s) and assign a letter to
each (capital letter for dominant, lower case letter for recessive)
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SOLVING GENETICS PROBLEMSGenetics Problems
Goal: to predict the traits of offspring1. Identify trait(s) and assign a letter to
each (capital letter for dominant, lower case letter for recessive)
2. Determine parents’ genotypes
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SOLVING GENETICS PROBLEMSGenetics Problems
Goal: to predict the traits of offspring1. Identify trait(s) and assign a letter to
each (capital letter for dominant, lower case letter for recessive)
2. Determine parents’ genotypes3. Draw Punnett square and fill in
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SOLVING GENETICS PROBLEMSGenetics Problems
Goal: to predict the traits of offspring1. Identify trait(s) and assign a letter to
each (capital letter for dominant, lower case letter for recessive)
2. Determine parents’ genotypes3. Draw Punnett square and fill in4. Determine the probabilities for
offspring of each genotype and phenotype
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SOLVING GENETICS PROBLEMSExample: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. Assign letters: tall = T short = t
2. Parents’ genotypesTrue breeding tall: TT True breeding short = tt
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SOLVING GENETICS PROBLEMS3. Draw Punnett Square
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SOLVING GENETICS PROBLEMS3. Draw Punnett Square
t t
T
T
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SOLVING GENETICS PROBLEMS3. Draw Punnett Square
Tt Tt
Tt Tt
t t
T
T
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SOLVING GENETICS PROBLEMS4. Calculate probabilitiesTT = _____Tt = ________tt = _________Tall = _________Short = _________ Tt Tt
Tt Tt
t t
T
T
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SOLVING GENETICS PROBLEMS4. Calculate probabilities10) TT = 0/4 Tt = 4/4 tt = 0/411) Tall = 4/4 Short = 0/4 Tt Tt
Tt Tt
t t
T
T
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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 = ____
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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.
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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: ___
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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: b2. White guinea pig: ___
Hybrid black guinea pig: ___
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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: b2. White guinea pig: bb
Hybrid black guinea pig: ___
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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: b2. White guinea pig: bb
Hybrid black guinea pig: Bb
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SOLVING GENETIC PROBLEMS
Bb bb
Bb bb
B b
b
b
3. Draw Punnett Square
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SOLVING GENETICS PROBLEMS4. Calculate probabilities BB = 0/4Bb = 2/4 (50%)bb = 2/4 (50%)
How many of the babies willProbably be Black = 10How many of the babies willProbably be White = 10
Bb bb
Bb bb
B b
b
b
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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
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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:
a) What is the mother’s genotype? ______ Father’s genotype? ____
b) What are their phenotypes? Mother: ___________ Father: _________
EEEe
AttachedAttached
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1) A MOTHER IS HOMOZYGOUS DOMINANT FOR EAR TYPE AND A FATHER IS HETEROZYGOUS: Draw a punnett square:
E
E
eE
EE
EE
Ee
Ee
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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: ____
Heterozygous: ____Homozygous Recessive:
____
E
E
eE
EE
EE
Ee
Ee
50%
50%
0%
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TONGUE ROLLING: DOMINANT If a mother can roll her tongue and a father
can not. What do we know about their genes?
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TONGUE ROLLING: DOMINANT
If a mother can roll her tongue and a father can not. What do we know about their genes?
Mother: _______Father: _______RR or Rr
rr only
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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?
c. Draw a punnett square:
r
r
rR
Rr
Rr
rr
rr
Yes!
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TONGUE ROLLING: DOMINANT
d. Which people in the family would be considered hybrids?
e. Are their any genotypes that this mother and father can not produce in their offspring? Why or why not?
Mom and the child that can roll their tongue
Yes, they can not produce a Homozygous Dominant (RR) child because the father only has recessive genes (r) to pass on
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CO AND INCOMPLETEDOMINANCE
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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
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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:
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CO-DOMINANCE
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FILL IN THE PUNNETT SQUARE
R
W
R
W RW RW
RW RW
Genotypes Phenotypes
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2. R= RED FURW= WHITE FUR
What do you think a RW cow will look like: ____________________
If the mother cow is homozygous red for fur color. What is her genotype: _____ Phenotype?________________
If the dad is homozygous white for fur color. What is his genotype: _____ Phenotype?________________
What percentage of the offspring will be RW: ______________
Red and White spots
RRRed Fur
WWWhite Fur
100%
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SOLVE THE FOLLOWING CROSSES: CO-DOMINANCE4. 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.
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PHENOTYPES
PP GG GP
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INCOMPLETE DOMINANCEThe heterozygous (Rr) Does not
look like the Homozygous recessive (rr) or the homozygous dominant (RR).
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INCOMPLETE DOMINANCE1. 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
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SOLVE THE FOLLOWING CROSSES: INCOMPLETE DOMINANCE
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B= BLACK (INCOMPLETE DOMINANCE)B = YELLOW (RECESSIVE)
What is the genotype for a dog that is Black : ______
What is the genotype for a dog that is Yellow :_____
What is the genotype for a dog that is Brown: ______
Show a cross between a Brown dog and a yellow dog.
BB
bb
Bb
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FILL IN THE PUNNETT SQUARE
B
b
b
b Bb bb
Bb bb
Genotypes Phenotypes
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WHAT PERCENTAGE OF THE PUPPIES ARE
BB=_________Bb=__________bb= __________
0%50%50%
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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: ____________
What do you think the genotype would be for the father sheep if he has black fur:_______________
What color would a Bb sheep be: __________________________
bb
BB
Gray
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FILL IN THE PUNNETT SQUARE
B
b
B
b Bb Bb
Bb Bb
Genotypes Phenotypes
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WHAT PERCENTAGES WILL THE F1 BE:
BB: _______% Bb: ________% bb: ________% Black:_________% White:_________% Hybrid: ________%
01000
00100