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Gregor Mendel
“The Father of
Genetics”
Sections 6.3, 6.4, 6.5
Language of Genetics
• Trait
Define the following 16 words
• Gene
• Allele
• genome
• Hybrid
• Genotype
• purebred
• Phenotype
• Test cross
• Homozygous
• Heterozygous
• Dominant
• Recessive
• F1 generation
• F2 generation
• P generation
Gregor Mendel
Born in 1822 in Austria
High School teacher at a
monastery
Avid gardener, studied pea
plants
Looked at different traits by
cross-pollinating the pea flowers.
The traits Mendel studied
in garden pea plants
The results of these studies lead to the
Three Basic Principles of Genetics
1. Principle of
Dominance
One gene in a trait can prevent the other
gene from being expressed.
Gene expressed is dominant B
Gene not expressed is recessive b
Dominant
genes
Remember
A trait is the same as an allele
which generally is the same as a gene
Today we call the
inherited traits genes!
2. Principle of
Segregation
The two genes for
each trait separate
when the gametes
are formed.
Each gamete only
carries one gene for
each trait
3. Principle of
Independent Assortment
Genes for different traits
can segregate independently
during the formation of gametes
Traits and Probability
Law of Probability
The probability of an event
occurring is not influenced by
the outcome of earlier events
There is always a 50% chance
of having a boy and a
50% chance of having a girl
Product Rule
The probability of two or more
independent events occurring
together is the product (x) of
the individual probabilities of
each occurring alone.
Probability of a coin being tails
is .5, for two coins to both be
tails is
.5 x .5 or .25
Now let us see how that applies
to predicting outcomes
in Genetic crosses
The Punnett
Square
The parents (P generation)
Have children (F1 generation)
The children (F1 generation)
cross with each other
and have children (F2 generation)
Monohybrid Cross
Genotypic ratio:
Phenotypic Ratio:
1 BB:2 Bb:1 bb
3 purple:1 white
Dihybrid Cross
A- yellow seed
a- green seed
B- round seed
b- wrinkled seed
Phenotypic ratio: 9:3:3:1
9 yellow round seeds: 3 yellow wrinkled seeds: 3 green round seeds: 1 green wrinkled seed