Genetics

1
Genetics
A study of inheritance
2
Objectives

• Understand
• Phenotype
• Genotype
• Dominance
• Gene Segregation
• Use a Punnett square to
• Solve monohybrid crosses
• Predict genotype ratio
• Predict phenotype ratio

3
Gregor Mendel

• Father of modern genetics

4
Gregor Mendel

• Father of modern genetics
• Researched with pea plants

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Gregor Mendel

• Father of modern genetics
• Researched with pea plants
• Developed ideas of dominance and trait segregation

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Phenotype

• Phenotype
• Physical characteristics

7
Genotype

• Phenotype
• Physical characteristics
• Genotype
• Genes we inherit from our parents

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Phenotype
Notice the similarities

• Facial structure
• Eyes
• Smile

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Phenotype
Notice the similarities

• Facial structure
• Eyes
• Smile
• Ears

10
Phenotype
Notice the similarities

• Facial structure
• Eyes
• Smile
• Ears
• Nose

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Phenotype
Notice the similarities

• Facial structure
• Eyes
• Smile
• Ears
• Nose
• Neck

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Mendelian Genetics

• Mendel studied a number of characteristics in pea
  plants including
• Height - short or TALL

13
Mendelian Genetics

• Mendel studied a number of characteristics in pea
  plants including
• Height - short or TALL
• Seed color - green or YELLOW

14
Mendelian Genetics

• Mendel studied a number of characteristics in pea
  plants including
• Height - short or TALL
• Seed color - green or YELLOW
• Seed shape - wrinkled or ROUND

15
Mendelian Genetics

• Mendel studied a number of characteristics in pea
  plants including
• Height - short or TALL
• Seed color - green or YELLOW
• Seed shape - wrinkled or ROUND
• Seed coat color - white or GRAY

16
Mendelian Genetics

• Mendel studied a number of characteristics in pea
  plants including
• Height - short or TALL
• Seed color - green or YELLOW
• Seed shape - wrinkled or ROUND
• Seed coat color - white or GRAY
• Pod shape - constricted or SMOOTH

17
Mendelian Genetics

• Mendel studied a number of characteristics in pea
  plants including
• Height - short or TALL
• Seed color - green or YELLOW
• Seed shape - wrinkled or ROUND
• Seed coat color - white or GRAY
• Pod shape - constricted or SMOOTH
• Pod color - yellow or GREEN

18
Mendelian Genetics

• Mendel studied a number of characteristics in pea
  plants including
• Height - short or TALL
• Seed color - green or YELLOW
• Seed shape - wrinkled or ROUND
• Seed coat color - white or GRAY
• Pod shape - constricted or SMOOTH
• Pod color - yellow or GREEN
• Flower position - terminal or AXIAL

19
Mendelian Genetics

• We will work with the following three
• Height - short or TALL
• Seed color - green or YELLOW
• Seed shape - wrinkled or ROUND
• Seed coat color - white or GRAY
• Pod shape - constricted or SMOOTH
• Pod color - yellow or GREEN
• Flower position - terminal or AXIAL

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Predicting Inheritance
To determine the chances of inheriting a given
trait, scientists use Punnett squares and symbols
to represent the genes. UPPERCASE letters are
used to represent dominant genes. lowercase
letters are used to represent recessive genes.
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Predicting Inheritance
For example T represents the gene for TALL in
pea plants t represents the gene for short in
pea plants So TT Tt both result in a TALL
plant, because T is dominant over t. t is
recessive. tt will result in a short
plant. Remember there are two genes for every
trait! One from each parent.
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Predicting Inheritance
For example T represents the gene for TALL in
pea plants t represents the gene for short in
pea plants So TT Tt both result in a TALL
plant, because T is dominant over t. t is
recessive. tt will result in a short
plant. Remember there are two genes for every
trait!
Mendels Principle of Dominance Some genes
(alleles) are dominant and others are recessive.
The phenotype (trait) of a dominant gene will be
seen when it is paired with a recessive gene.
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Predicting Inheritance
Lets cross a totally dominant tall plant (TT)
with a short plant (tt). Each plant will give
only one of its two genes to the offspring or F1
generation. TT x tt
T
T
t
t
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Predicting Inheritance
Lets cross a totally dominant tall plant (TT)
with a short plant (tt). Each plant will give
only one of its two genes to the offspring or F1
generation. TT x tt
Mendels Law of Segregation Each gene (allele)
separates from the other so that the offspring
get only one gene from each parent for a given
trait.
T
T
t
t
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Tt
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TT
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tt
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Homozygous recessive
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Heterozygous
30
Homozygous dominant
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Pure bred dominant
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hybrid
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Purebred recessive
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Punnett Squares

Tt Tt
Tt Tt
The genes from one parent go here.
The genes from the other parent go here.
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Punnett Squares
T T
t Tt Tt
t Tt Tt
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Punnett Squares
T T
t Tt Tt
t Tt Tt
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Punnett Squares
T T
t Tt Tt
t Tt Tt
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Punnett Squares
T T
t Tt Tt
t Tt Tt
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Punnett Squares
T T
t Tt Tt
t Tt Tt
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Punnett Squares
T T
t Tt Tt
t Tt Tt
F1 generation
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Interpreting the Results
The genotype for all the offspring is Tt. The
genotype ratio is Tt - 4/4 The phenotype for
all the offspring is tall. The phenotype ratio
is tall - 4/4
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Punnett Squares
T t
T ?? ??
t ?? ??
Your Turn!!
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Punnett Squares
T t
T TT Tt
t Tt tt
F2 generation
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Punnett Squares
Next, give the genotype and phenotype ratios of
the offspring (F2 generation).
T t
T TT Tt
t Tt tt
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Punnett Squares
Genotype ratio TT - 1
T t
T TT Tt
t Tt tt
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Punnett Squares
Genotype ratio TT - 1, Tt - 2
T t
T TT Tt
t Tt tt
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Punnett Squares
Genotype ratio TT - 1, Tt - 2, tt - 1
T t
T TT Tt
t Tt tt
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Punnett Squares
Genotype ratio TT - 1, Tt - 2, tt - 1
T t
T TT Tt
t Tt tt
Phenotype ratio Tall - 3
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Punnett Squares
Genotype ratio TT - 1, Tt - 2, tt - 1
T t
T TT Tt
t Tt tt
Phenotype ratio Tall - 3, short - 1
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Punnett Squares
T t
T TT Tt
t Tt tt
This is a monohybrid cross. We worked with only
one trait. The height of the plant.
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Punnett Squares
T t
T TT Tt
t Tt tt
This is a monohybrid cross. We worked with only
one trait. The height of the plant.
two
Later we will work with a dihybrid cross, using
the height of the plant and either seed color or
seed shape.
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Homework - Punnett Squares
T t
T TT Tt
t Tt tt
Questions 1 2 on Rats Practice Problems and
question 1 on Foxes and Watermelons Practice
Problems.