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Genetics
Biology 2009
Gregor Mendel and the Garden Pea (page 117)
Genetics: the study of heredity; how an offspring gets traits
from their parents.
Describe Gregor Mendel.
Who? Monk (priest)
What? Curious gardener trained in math and science
When? 1860s
Where? Austria
How did Mendel add a “twist” to his research? He used math
to draw conclusions from his observations.
List 4 reasons why the garden pea was a good subject
for scientific study.
1. easy to grow
2. grow quickly
3. large number of offspring; a lot of quantitative
data
4. plants have both male and female parts;
fertilization can be controlled
Define self-fertilization: plant that fertilizes itself
Define cross-fertilization: plant that is fertilized by
another plant
Mendel’s Experiment (page 118)
Step One: Creating the parent (P) generation (Pure
Breeding)
• allowed plants to self-fertilize for many generations
• collected and grew the seeds from the plants
• observed that purple flowering seeds grew purple
flowers and white flowering seeds grew white flowers.
CREATED PURE BREEDING PLANTS
Step Two: Cross breeding plants from parent
generation to create F1 generation.
• used pollen from purple flower and fertilized white
flower
• collected and grew seeds
• only purple flowers grew from this generation.
Results of Step Two: When Mendel cross fertilized a true breeding
purple plant with a true breeding white plant, all of the offspring had
purple flowers.
Mendel asks…Where did the white flowers go?
Hypothesis…even though the flowers were all purple, they must be carrying around
some kind of white flowering plant “factors”.
Step Three: Self-pollinate one of the offspring from
the F1 generation to create the F2 generation.
• self-fertilized a purple flowered plant from the F1
generation
• collected and grew the seeds
• purple and white flowers showed up on the plants
For every 4 flowers on the plants, 1 one was white and
3 were purple.
3:1 Ratio in the F2 generation
Mendel’s Quantitative Results:
Total Pea Plants in F2 Generation = ___________
Pea Plants with Purple Flowers = ___________
Pea Plants with White Flowers
= ___________
What % of Mendel’s F2 Generation had purple flowers?
(purple flowers / total flowers) x 100 = __________%
What % of Mendel’s F2 Generation had white flowers?
(white flowers / total flowers) x 100 = ___________%
The ratio of purple to white flowers in Mendel’s
F2 Generation is ____ : _____.
List three other pea plant traits that Mendel studies.
1.
2.
3.
Mendel’s Experiments (page 119)
Use Table 7-1 on page 119 to complete the missing boxes in the chart
below.
Contrasting Traits in Pea Plants
Trait
Flower Color
Contrasting Form F2 Generation Ratios
of Traits
Purple and White
Seed Color
705:224
Purple
6,022:2,001
Yellow
Round and
Wrinkled
Pod Color
Which trait showed
up more often?
Round
428:152
Mendel’s Explanation of the Results (VERY IMPORTANT
VOCABULARY)
Factors: “information” that is trasfered from parent to offspring
Traits: characteristic you get from your parents (ex: hair color)
Alleles: different forms of this information; types of traits (ex:
brown vs. blonde)
Principle of Dominance: some alleles are more dominant than others
Dominant Traits: traits that show up more often in a population;
stronger allele (ex: brown eyes)
Recessive Traits: traits that show up less often in a population;
weaker allele (ex: red hair)
Genotype: type of alleles passed from parent to offspring
Homozygous (pure bred): contain two of the same allele for a
trait (ex: both parents pass brown eyes to their offspring
Heterozygous (hybrid): contain two different alleles for a trait
(ex: one parent passed brown eyes and the other passed blue
eyes)
Dominant Allele + Dominant Allele = dominant trait
Dominant Allele + Recessive Allele = dominant trait
Recessive Allele + Recessive Allele = recessive trait
Phenotype: physical appearance of a trait (brown eyes)
Section 7-1 Quiz
The Principle of Dominance Related to some Simple
Human Traits
TRAIT
Tongue rolling
Skin
appearance of
freckles
Hairline
Dimples
PTC
Ear lobe
Bent fingers
Thumb
Finger hair
Your Phenotype
Dominant
trait?
Recessive
trait?
Class Ratio
Dominant to
Recessive
Frequency %
of your trait
Mendel’s Conclusions (page 122)
Law of Segregation: when gametes (sex cells) are made, the
two alleles for each trait will separate; gametes only carry
one of each allele.
Law of Independent Assortment: alleles for different traits
segregate into gametes (sex cells) independently from one
another
Bill Nye: Understanding Basic Genetics
Segregation of Alleles and Fertilization of Gametes
Directions: Complete each chart using the given information. Collect quantitative
data using the information within the completed chart.
1. True breeding Yellow Seeds x True Breeding Green Seeds
Dominant Trait: ______________ Domiant Allele: _____
Recessive Trait: ______________ Recessive Allele: _____
# Dominant _________
# Recessive _________
% Dominant _________
% Recessive ________
Ratio ____: ____
Segregation of Alleles and Fertilization of Gametes
Directions: Complete each chart using the given information. Collect quantitative
data using the information within the completed chart.
2. Hybrid Green Pea Pod x Hybrid Green Pea Pod
Dominant Trait: ______________ Domiant Allele: _____
Recessive Trait: ______________ Recessive Allele: _____
# Dominant _________
# Recessive _________
% Dominant _________
% Recessive ________
Ratio ____: ____
Segregation of Alleles and Fertilization of Gametes
Directions: Complete each chart using the given information. Collect quantitative
data using the information within the completed chart.
3. True Breeding Round Seed x Hybrid Round Seed
Dominant Trait: ______________ Domiant Allele: _____
Recessive Trait: ______________ Recessive Allele: _____
# Dominant _________
# Recessive _________
% Dominant _________
% Recessive ________
Ratio ____: ____
Segregation of Alleles and Fertilization of Gametes
Directions: Complete each chart using the given information. Collect quantitative
data using the information within the completed chart.
4. True Breeding Wrinkled Seeds x True Breeding Round Seeds
Dominant Trait: ______________ Dominant Allele: _____
Recessive Trait: ______________ Recessive Allele: _____
# Dominant _________
# Recessive _________
% Dominant _________
% Recessive ________
Ratio ____: ____
Punnett Square: diagram used to show genetic crosses (segregation and
fertilization of alleles)
Probability: the likelihood that something will happen
Visualizing Mendel’s Model (pages 120-1)
•Choose a letter to represent the trait being modeled
•Upper case letter represents dominant form of trait (dominant allele)
•Lower case letter represents recessive allele
•Parent genotypes go on the outside of the box (segregating one allele to each box)
•Offspring genotypes (fertilized together) go on the inside of the boxes
Punnett Square Modeling Mendel’s Parent to F1
Generation: Flower Color
Phenotype of the Parent Generation: _______and_____________
Genotype of the Parent Generation: _______and_____________
Punnett Square Modeling Mendel’s F1 to F2 Generations: Flower
Color
Phenotype of the Parent Generation: _______and_____________
Genotype of the Parent Generation: _______and_____________
Sponge Bob Genetics
Punnett Square Quiz
Law of Independent Assortment: Alleles for different traits
segregate independently of one another when sex cells are
made.
For Example: What happens if a man who is heterozygous brown eyes AND
heterozygous tongue roller has children with a woman who is homozygous blue
eyes AND heterozygous tongue roller?? What is the chance that their child will
be a blue eyed non-tongue roller?
Due to Mendel’s Law of Independent Assortment, we must look at all possible
allele combinations that can go into sperm and egg. We will use a method of
distribution you may have seen in math class called FOIL. FOIL stands for First,
Outside, Inside, Last.
Foil the following genotype: BbWw
(F) _____, (O) ______, (I) _____, (L) ____
Now we’re ready to tackle the example problem above.
What happens if a man who is heterozygous brown eyes AND heterozygous
tongue roller has children with a woman who is homozygous blue eyes AND
heterozygous tongue roller??
Dad’s Genotype: ____________
Possible Sperm Alleles: ______ or _______ or ______ or _______
Mom’s Genotypes: _____________
Possible Egg Alleles: ______ or _______ or _______ or _________
What is the chance their child will be a blue-eyed non-tongue roller?
______ out of _____ or ______%
Dad: Homozygous blue eyes AND Heterozygous Widow’s Peak ____________
Mom: Heterozygous brown eyes AND Heterozygous Widow’s Peak ___________