UNDERSTANDING
INHERITANCE
Traits
Detached Earlobes
Tongue rolling
Dimples
Cleft Chin
Cross Left thumb over right
See Colours Red and Green
Straight Hair Line vs Widows Peak
Key Terms
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Selective breeding
Artificial breeding
Pure Bred
Gregor Mendell
Traits
Self-fertilization vs. Cross Fertilization
Monohybrid cross
Dihybrid cross
P generation
F1 and F2 generation
Dominant vs. recessive traits
Genotype vs. Phenotype
Heterozygous and Homozygous alleles
Early Genetics
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Selective breeding was the earliest form of
understanding about genetics
Selective breeding (a form of artificial breeding) is
when people breed certain animals or plants in
order to produce a desired offspring
For example: Horses that developed strong muscles
were bred with other horses that had strong muscles
in order to make race horses.
Early Genetics
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Pure bred horses are used by horse breeders to
produce offspring that are quicker, stronger, and
more durable for races.
Early Genetics
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Prior to the 1850’s and 1860’s people did not understand
how genetics worked.
In the 1600’s, live sperm was discovered using a microscope.
It was believed that a tiny person was inside the sperm and
that this person would develop inside the mother
In the 1800’s, scientists realized that people inherit their
characteristics from both parents.
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However, they believed in blended inheritance (i.e. if mother has
blond hair and father has black, the child will have brown hair.
Gregor Mendel – The Pioneer of
Genetics
Gregor Mendel: The Pioneer of
Genetics
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Gregor Mendel was the first to conduct a scientific
experiment on inheritance
Mendel discovered inheritance by studying garden
peas
Gregor Mendel’s Observations
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Gregor Mendel noticed that some garden pea
plants were tall while others are short, some pea
plants had different flower position…
Gregor Mendel’s Observations
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… some pea plants were round while others were
wrinkled, and some pea pods were full while others
flat
Mendel referred to these characteristics as traits.
Gregor Mendel’s Observations
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Mendel also noticed that pea plants could selffertilize and cross-fertilize.
Self-fertilization means that a plant is able to
reproduce with itself and produce offspring.
Cross-fertilization means that a plant reproduces
with another plant to produce an offspring (sexual
reproduction).
Cross-Fertilization Vs. Self-Fertilization
Mendel’s Experiment
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Mendel used pea plants that self-fertilize for his
experiment.
 This
meant that the offspring made by that plant will be
the same as the parent
 This is referred to as true breeding or pure breeding.
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Mendel then selectively fertilized a pure bred green
pea plant with a pure breed yellow pea plant.
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Genetics this is called a cross. (a.k.a cross fertilization)
Mendel’s Experiment
Cross Fertilization
Before we look at
the results let us
clarify some key
terms
Key Terms
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Since Mendel was only examining the colour of the
pea pod, it is called a monohybrid cross.
If for instance Mendel was examining both the
colour and the size of the pea plant, then it would
be called a dihybrid cross.
Key Terms
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In a test cross (cross
pollination) the parent
generation is called P
generation
The first offspring is called
F1 generation
The children of the F1
generation is the F2
generation.
…And so forth…
Back to the results
of Mendel’s
Experiment
Mendel’s Results
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When Mendel cross fertilized pure bred green pea
plants with pure bred yellow pea plants
 The
offspring were all green pea plants.
Mendel’s Experiment
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Through this experiment Mendel realized that some
traits (i.e green coloured pea plants) are dominant
to other traits (i.e. yellow coloured pea plants).
The green coloured allele for pea plants is
therefore dominant to the yellow coloured allele.
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The yellow coloured allele is therefore recessive.
Mendel’s Experiment (Part 2)
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Mendel then crossed two of the F1 generation pea
plants from the original experiment and…
 The
result was that ¾ of the offspring were green and
¼ were yellow
Genotype vs. Phenotype
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Alleles are often represented using upper-case
letters and lower-case letters.
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Recall Mendel’s experiment:
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Which colour allele is dominant?
Genotype
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Since the green allele is dominant, we can represent
it using the letter G.
On the other hand, the yellow allele is recessive and
we can represent it using the letter g.
Remember each trait has 2 alleles:
 This
makes it possible to have 3 different combinations:
1. GG
2.Gg
3. gg
Let us look at a
different
example
Genotype vs. Phenotype
Genotype vs. Phenotype
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Genotype refers to the combination of alleles and
the phenotype refers to the physical characteristics
(e.g. observable traits) produced by the alleles.
Genotype
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If the gene contains two dominant alleles (e.g. GG)
we call this genotype homozygous dominant.
If the gene contains two recessive alleles (e.g. gg)
we call this genotype homozygous recessive.
If the gene contains one dominant and one recessive
allele (e.g. Gg) we call this genotype
heterozygous.
Genotype vs. Phenotype
HOMEWORK
Pg.207 # 4, 6, 9, 11